How would this algebra equation be solved

I simplified the original problem to: 21u - 35 = -18u + 90

Can someone walk me through this equation? thanks.

21u - 35 = -18u + 90
21u - 35 + 18u = 90 add 18u to each side
21u + 18u = 90 + 35 add 35 to each side
39u = 125 perform the additions on each side
u = 125 / 39 divide each side by 39
u = 3 8/39 reduce right side to a mixed number

Bring all the "u" terms to the left, and all the non "u" to the right.

21u+18u=35+90

Factor out the "u" on the left

u(21+18)=35+90

Divide by (21+18)

u= (35+90)/(21+18)

21u+18u=35+90
39u=125
u=125/39