I NEED HELP WITH THIS ITS ABOUT REBOUND RATIO

Alicense plate is to consist of 44 digits followed by 55 uppercase letters. determine the number of different license plates possible if the first and second digits must be? odd, and repetition is not permitted.

Aswimming pool has an input pump for filling the pool and an output pump for emptying the pool. the input pump can fill the pool in 3 hours, and the output pump can drain the pool in 5 hours. as you go to bed, the pool is full, but a neighbor’s kid turns on the output pump. at midnight, you awake to find the pool half empty. immediately, you turn on the input pump, but you are sleepy and forget to turn off the output pump. at what time will the pool become full?

Solve x+3y=6 and 4x-6y=6 by elimination . show work !