As you might've noticed, there is a PATTERN in the number of termites. That pattern is the no. of termites MULTIPLIED BY 4. Let me prove this:
The 1st term in the no. of termites is 70, the 2nd is 280. 70 MULTIPLIED BY 4 IS 280, ISN'T IT? Now let's look at the 2nd term in the no. of termites is 280 and the 3rd term is 1,120. 280×4= 1,120 isn't it?
Therefore after 1 year the no. of termites is 1, 174,405, 120.