Question

2/3 over 10 equals 1.8/r solve for r.

(2/3)/10 = 1.8r.
First, invert and multiply the denominator; i.e.,10.
(2/3)*(1/10) = 1.8/r
2/30 = 1.8/r
Now cross multiply.
2r = 30*1.8
2r = 54
Now divide both sides by 2
2r/2 = 54/2
r = 27
check my thinking. check my work.