check the picture below.
so it has a base of 18x18 and a height of that much.

Answer: 14.6
Step-by-step explanation:
I made a square around the triangle which I then counted the squares, found the Pythagorean theorem, and then added the missing sides together
The formula for the sum of n terms in an arithmetic progression is:
S = n/2 * (2a + (n-1)d)
Here, the common difference, d, is 8 and the first term, a, is 1. Substituting these into the formula, we get:
S = n/2 * (2*1 + 8(n - 1))
S = n + 4n² - 4n
S = 4n² - 3n
The answer is A.
Point E is correct answer