The answer is 14
0.4r-7=-.3r+2.8
Add 7 to both sides. -7+7=0 so it cancels on the left. 2.8+7=9.8.
0.4r=-.3r+9.8.
Add .3r to both sides. -.3r+3r=0 so it cancels on the right. 0.4r+.3r=0.7r.
0.7r=9.8
Divide 0.7 to both sides. 9.8 divided by 0.7 = 14
So r=14