Move all terms not containing f to the right side of the equation.
Subtract 21 from both sides of the equation.
Subtract 21 from 75.
Divide each term by 3 and simplify.
Divide each term in 3f=54 by 3.
Cancel the common factor of 3.
Cancel the common factor.
Divide f by 1.
Divide 54 by 3.
Solve for f 21+3f=75