Draw a circle around the ratio that is NOT EQUIVALENT to 6 to 10

1. 9 : 15

2. 3 : 15

3. 18 : 30

4. 5 : 3

i have been struggling all day, please help a sad girl out:)

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?

Can some one explain this i got sent this. is this a threat i’m scared

What is the solution for 6 - 7/8? explain the steps.