Answer:
Part A:
The problem doesn't say if it's a right triangle, but it seems like it is.
for right angle triangles, the Pythagorean theorem applies:
a^2 + b^2 = c^2, where a & b are the legs of the triangle, and c is the hypotenuse.
12^2 + 35^2 = 144 + 1225 = 1369, and the square root of 1369 = 37.
Part B:
Andres thought the equation was a^2 + b^2 = c, or he forgot to find the square root of 1369.