3
of a number is 21.
5
Find the number

w = -20

Step-by-step explanation:

-+ 9 = 13

Shift the (+9) to the other side of the equation. (+9) will turn into (-9).

- = 13 - 9

   = 4

Shift the (÷5) to the other side of the equation. (÷5) will turn into (×5).

-w = 4 × 5

    = 20

Multiply both sides of the equation by (-1) so that -w will turn into w.

w = (-1) × 20

w = -20