3f-6+9f=-21

Solution for 3f-6+9f=-21 equation:

Simplifying
3f + -6 + 9f = -21

Reorder the terms:
-6 + 3f + 9f = -21

Combine like terms: 3f + 9f = 12f
-6 + 12f = -21

Solving
-6 + 12f = -21

Solving for variable 'f'.

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

Add '6' to each side of the equation.
-6 + 6 + 12f = -21 + 6

Combine like terms: -6 + 6 = 0
0 + 12f = -21 + 6
12f = -21 + 6

Combine like terms: -21 + 6 = -15
12f = -15

Divide each side by '12'.
f = -1.25

Simplifying
f = -1.25