210= 84/(R1/2+R1/3)

solve for R1

How do I do this

210= 84/(R1/2+R1/3)

Multiply both sides by the denominator, assuming that R1 ≠ 0:
210(R1/2+R1/3)=84
Now find the common denominator of 2 and 3 to get:
210(3R1+2R1)/6 = 84
Multiply both sides by 6/210 and simplify:
5R1 = 12/5
R1 = 12/25