In formula for where ferenheit and celsius converge (T = T x 9/5 +32); what is the logic that T x 9/5 = T + T = 4/5?

I'm confused. I don't know that there is any logic to that but there may be if we spend enough time on it. If I were doing it I would write

(9/5)C + 32 = F
We want C = F; therefore,
(9/5)C + 32 = C
Multiply through by 5 to obtain
9C + 160 = 5C
9C-5C = -160
4C = -160
C = F = -40