To solve this problem we just have to add the opposite number to the number inside the parenthesis (next to the blank space) on both sides of the equation, the x will represent the blank space
a)
The unknown number is 59.
b)
The unknown number is -14.
c)
The unknown number is -32.
d)
The unknown number is -12.
e)
The unknown number is -13.
f)
The unknown number is -21.