We are given the equation,
[tex] j= 4rb [/tex]
Here we have to solve for r.
r is in multiplication with 4b on the right side of equation.
So we apply opposite operation of multiplication on the left side.
opposite operation of multiplication is division.
So dividing left side by 4b,
[tex] \frac{j}{4b} =r [/tex]
So answer is r=j/4b.