Answer:
39
Step-by-step explanation:
These are all right angles. This means they have a total value of 90 degrees.
The first problem would resolve like this:
b + 51 = 90
b = 39
Problem 6 would be as follows:
3x + 6 + 48 = 90
3x + 54 = 90
3x = 36
x = 12