21=W(W+4)

Solution for 21=W(W+4) equation:

Simplifying
21 = W(W + 4)

Reorder the terms:
21 = W(4 + W)
21 = (4 * W + W * W)
21 = (4W + W2)

Solving
21 = 4W + W2

Solving for variable 'W'.

Reorder the terms:
21 + -4W + -1W2 = 4W + -4W + W2 + -1W2

Combine like terms: 4W + -4W = 0
21 + -4W + -1W2 = 0 + W2 + -1W2
21 + -4W + -1W2 = W2 + -1W2

Combine like terms: W2 + -1W2 = 0
21 + -4W + -1W2 = 0

Factor a trinomial.
(3 + -1W)(7 + W) = 0

Subproblem 1
Set the factor '(3 + -1W)' equal to zero and attempt to solve:

Simplifying
3 + -1W = 0

Solving
3 + -1W = 0

Move all terms containing W to the left, all other terms to the right.

Add '-3' to each side of the equation.
3 + -3 + -1W = 0 + -3

Combine like terms: 3 + -3 = 0
0 + -1W = 0 + -3
-1W = 0 + -3

Combine like terms: 0 + -3 = -3
-1W = -3

Divide each side by '-1'.
W = 3

Simplifying
W = 3
Subproblem 2
Set the factor '(7 + W)' equal to zero and attempt to solve:

Simplifying
7 + W = 0

Solving
7 + W = 0

Move all terms containing W to the left, all other terms to the right.

Add '-7' to each side of the equation.
7 + -7 + W = 0 + -7

Combine like terms: 7 + -7 = 0
0 + W = 0 + -7
W = 0 + -7

Combine like terms: 0 + -7 = -7
W = -7

Simplifying
W = -7
Solution
W = {3, -7}