Algebra - show all work

Question

Pipe A can fill a tank in 25 minutes. Pipe B can fill a tank in 20 minutes. To fill the empty tank, Pipe A was opened alone for 3 minutes and, after that, Pipe B was also opened. How much time will it take for both Pipes A and B to finish filling the tank?

Answer 1

rate a=(1/25)

rate b=(1/20)

me assume yu meen yu open a for 3 min, then both pipes floe at same time

3*(1/25) +x[(1/20)+(1/25)]=1 tank full

(3/25)+x(0.05+0.04)=1

0.09x=1-0.12

0.09x=0.88

x=0.88/0.09

x=9.7777777777777777...

or 9 & 7/9 minute