Could someone explain in detail how you get from the first l

Could someone explain in detail how you get from the first line to the second?

100 = 1/0.0085 + 2/r_0 r_0 = 200/1 - 100 Times 0.0085 = 200/0.15 = 1333 Ohm

100 = 1/[0.0085 + 2/r]

multip;ly both sides with [0.0085 + 2/r]

100[0.0085 + 2/r] = 1

0.85 + 200/r = 1

200/r = 1-0.85

200/r = 0.15

multiply both sides with r

So, 200 = 0.15r

r = 200/0.15 = 1333.33 = 1333 ohm