Question 872675
Let:

1/25    - is the part A makes in a minute
1/18    - is the part B makes in a minute

{{{1/25+1/18=43/450}}}

43/450 is the part they can do together in a minute.

Now I'll let "t" stand for how long they take to do the job together. Then they can do 1/t per hour, so 43/450 = 1/t. Flip the equation, and you get that t = 450/3 or 150.

{{{1/25+1/18=1/t}}}
{{{43/450=1/t}}}
{{{t=150}}}

They can complete the job together in 150 minutes! :)