Basic Algebra Problem(s)?

Question

I have a little sheet to work on to refresh my old algebra skills, and i always had trouble with fractions, can anyone help? I Don't want the answers, i end up always looking for the wrong thing and missing a step. i just want the steps on what to do/look for so if i ever have to do it again, it won't be a problem. Help?

: 3/4(a)=9

: 4/5(a)=-20

: -9(b)=2

Answer 1

3/4(a)= 9

times both sides by 4= 3(a)= 9X4

divide both sides by 3= a= (9X4)/3

so a= 12

following the same principle do the rest

5/5(a)= -20

a= (-20X5)/5 so a= -20

-9(b) = 2

b= 2/-9 so b= -0.2222

Answer 2

when you isolate for a in the first two, you have to divide both sides by the fraction. Dividing a fraction is the same as multiplying it's reciprical, so 9 divided by 3/4 is 9 times 4/3, or 9/1 times 4/3. Then just multiply top by top, bottom by bottom, and simplify. Same with the second one. The third, just divide both sides by -9.