(for this answer i'm gonna use 0 to make it easier firstly you have to reoder the terms like this : 18 + 3 (-13+9f)=0 then you multiply -13 and 9f by 3 like this : 18 + (-13 x 3 + 9f x 3)=0 and it should be like this: 18 + (-39 + 27f)=0 Next you have to combine like terms which is: 18 + -39 and you will get -21 and you add it to 27f which is: -21 + 27f=0 and you have to solve for the variable f and move all the terms containing f to the left and all other terms to the right.
