A triangle will have a total of 180 degrees.
Since it is a right triangle, we know that one angle is 90 degrees. We also know that one of the other angles is 51.
90 + 51 + x = 180
141 + x = 180
Subtract 141 on both sides.
x = 180 - 41
x = 39
The value of b is 39 degrees.
