Measure of angle b=(3x+10) and measure of angle a=x if angle c is a right angle what is the value of x

x = 20

Form your equation => <C = 90 because it is a right angle.
(3x + 10) + (x) + 90 = 180
      ^           ^      ^        ^
   <B         <A   <C      All angles (A, B, C) add up to 180 because of the Triangle                                    Sum Theorem.

Solve the equation.
3x + 10 + x + 90 = 180          Combine like terms
4x + 10 + 90 = 180                Combine like terms
4x + 100 = 180                      Subtract 100 from both sides
4x = 80                                 Divide by 4 to both sides
x = 20                                   Answer!