In the expression below if a = 4, what value of b is needed for the expression to have a value of 81?

12a3b7(ab)-4

1 answer

12(4)3b7(4) - 4

144b + 125 - 4

144b + 121

To find the value of b that makes the expression equal to 81, we can solve the equation:

144b + 121 = 81

Subtract 121 from both sides:

144b = 81 - 121

144b = -40

Divide both sides by 144:

b = -40/144

Simplifying the fraction:

b = -5/18

Therefore, the value of b needed for the expression to have a value of 81 when a = 4 is -5/18.