Q=3 (r+1) / r

Make r the subject of the formula

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)