21=2(y+3)

Solution for 21=2(y+3) equation:

Simplifying
21 = 2(y + 3)

Reorder the terms:
21 = 2(3 + y)
21 = (3 * 2 + y * 2)
21 = (6 + 2y)

Solving
21 = 6 + 2y

Solving for variable 'y'.

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

Add '-2y' to each side of the equation.
21 + -2y = 6 + 2y + -2y

Combine like terms: 2y + -2y = 0
21 + -2y = 6 + 0
21 + -2y = 6

Add '-21' to each side of the equation.
21 + -21 + -2y = 6 + -21

Combine like terms: 21 + -21 = 0
0 + -2y = 6 + -21
-2y = 6 + -21

Combine like terms: 6 + -21 = -15
-2y = -15

Divide each side by '-2'.
y = 7.5

Simplifying
y = 7.5