Hello there, this problem is just basic addition, here is what it would look like

Solve it and we get 78.21
For the first 60 positive integers, a = 1, n = 60, l = 60.
Sn = n/2(a + l)
s = 60/2(1 + 60) = 30(61)
For the next 60 positive integer, a = 61, n = 60, l = 120
Sum = 60/2(61 + 120) = 30(61 + 120) = 30(61) + 30(120) = s + 3600
Sum of first 120 positive integers = s + s + 3600 = 2s + 3600
2x-14=-3x+6
You need to combine like terms and get all the x's on one side and the numbers on the other
2x+3x-14=6
5x=6+14
5x=20
now divide to get x alone
x=4
Hope that helps