Distribute the 3 to the parentheses. Q=3r+3/r
Next multiply both sides by r to get rid of the division sign.
Qr=3r+3
Subtract 3r on both sides and you get Qr-3r=3
Since both numbers have an r in it, we can factor out the r
r(Q-3)=3
Then we divide Q-3 on both sides
r=3 / (Q-3)