Because the sum of the interior angles of a triangle are equal to
180 degrees, add 120 and 40 to get 160, then subtract from 180. Your answer would be
<B = 20 degrees. To find out which side is the longest, draw a triangle with angles that are close to these angle measurements. The side across from <A (the largest angle) is the longest side. Depending on your drawing, the longest side would either be
BC or CB, depending on your letter order.
Hope this helps!! :)