This should help you here are the steps of your problem :)
2*(1/2)*r+2*r+1 = 9*(1/10) // - 9*(1/10)
2*(1/2)*r+2*r-(9*(1/10))+1 = 0
2*(1/2)*r+2*r-9/10+1 = 0
3*r+1/10 = 0 // - 1/10
3*r = -1/10 // : 3
r = -1/10/3
r = -1/30
r = -1/30
So your answer would be 1/30
