Question 10505
You started out fine, but went a little astray on the way down.

0.4r - 1.2 = 0.3r + 0.6  Multiply through by 10 to clear the decimals.
4r - 12 = 3r + 6 Add 12 to both sides.
4r = 3r + 18 Subtract 3r from both sides.
r = 18

Check:

0.4(18) - 1.2 = 0.3(18) + 0.6
7.2 - 1.2 = 5.4 + 0.6
6 = 6 The solution (r = 18) is correct.