The sum of the first 90 positive integers can be found using the formula:

sum = (n/2)(first + last)

where n is the number of terms, first is the first term, and last is the last term.

In this case, n = 90, first = 1, and last = 90. Substituting these values into the formula, we get:

sum = (90/2)(1 + 90)
sum = 45(91)
sum = 4095

Therefore, the sum of the first 90 positive integers is 4095.