Answer: The other two sides are both 80 in.
Explanation: The sides of a triangle always add up to make 180, a straight angle. Since you said the longest side, we assume this is an isosceles triangle; therefore, the other two sides are the same length. So,
180-20=160
160 is the remaining length we have after taking away the 20 inches.
160/2=80
Since the other two sides are the same length, we divide 160 by 2 to get an equal amount of length.