Find the first positive term of the arithmetic progression (an): a4 = -71, d = 0.5.

Divide 71 by 0.5 to find out how many times you need to add the progression difference to (- 71) to get zero.

71: 0.5 = 142.

We find out the number of that member of the progression, which is 142 steps away from the fourth.

4 + 142 = 146.

Let’s find the value of the 146th term of the progression.

a146 = a4 + 142 * 0.5 = – 71 + 71 = 0.

The next 147th term in the progression will be positive.

Answer: a147 = 0.5.