One complete solar year is 365.2425 days
12 lunar months at 29.53059 days is equal to 354.36708 days
The difference between the two is 10.87542 days.
Dividing that in half to get the average is 5.43771
354.36708 + 5.43771 = 359.80479 - 359 plus 19.2 hours – that is in the 360th day.
365.2425 – 5.43771 = 359.80479 – 359 plus 19.2 hours – that is in the 360th day.
or 365.2425 (solar) + 354.36708 (lunar) = 719.60958 / 2 = 359.80479 which is 359 days 19 hours and about 10 minutes. Or IN the 360th day.
In other words, this is the average length of the year between both the lunar and the solar and it is the same – 360 days x 3.5 years is 1260. To be more exact that is 359.80479 x 3.5 = 1259.316765; 1259 days 7 hours and about 36 minutes. Or IN the 1260th day.
(the .80 of a day is = 19.2 hours. 359 days 19 hours and about 10 minutes. 365.25 - like the .25 = one quarter of a day or 6 hours)
1260 divided by the average of 30 equals 42 months.
Here is an interesting fact that can show us that the months do not have to change from our common 29.53 to an even 30-days per lunar month. In other words, concerning the two witnesses who will prophecy 1260 days it can be shown that they can begin to prophecy at one appointed time and end on another. We have done the math from two starting points.
The first one is from Yom Kippurim (2014) counting 1260 days forward would put us on 3/17/18 - equalling the first day of the solar year.
But what is even more interesting is if we count from the Last Great Day (2014) counting forward 1260 days puts us on the 12th of Abib - that could be the day that the two witnesses are killed (in other words they're killed on the 1260th day of their witnessing) and they lay dead in the streets for 3.5 days. If they were killed at evening on the 12th, 3 and a half days later would be at the beginning of the 16th day; which is also the day of the wave omer - first fruits. Remember Yahusha rose early in the morning on the first day of the week.
If they were killed at the very end of the 12th day, which would be beginning the 13th day of the month, then they would be dead in the streets the 13th, 14th, 15th, and half way through the 16th. Remember what happened half way through the 16th on the the day Yahusha was raised? The first fruits of the Set-apart Spirit was given the evening of that day.