An isosceles triangle has two equal sides that are each 3 more than the length of the base. If the perimeter of the triangle is 45, what…

Let the base be $b$. Each equal side is $b + 3$. The perimeter is $b + 2(b + 3) = 45$, so $3b + 6 = 45$, then $3b = 39$ and $b = 13$, choice D. Check: the sides are 13, 16, and 16, which sum to 45. Choice A (14) gives sides 14, 17, 17, which sum to 48. Choice B (16) is the length of an equal side, not the base. Choice C (15) comes from dividing 45 by 3 and assuming an equilateral triangle. Make sure to identify which side the question asks about.