Question

If 21 is added to a number the result is 40 less than twice the number what is the number?

Answer 1

If 21 is added to (+ 21) a number (x) the result (=) is 40 less than (- 40) twice the number (2x)

x + 21 = 2x - 40   Add 40 to both sides
x + 61 = 2x           Subtract x from both sides
      61 = x             Switch the sides to make it easier to read
       x = 61