Hi! :)
It sounds like you need to multiply this fraction.

*16=6
So, Marge used 6 total inches of tape.
Hope this helps!
You will save $9
Convert 20% to decimal
Each % is 0.01 so 20×0.01=0.2
Then multiply
45×0.2=9
If you’re looking for the ratio:
75cm = 750mm
250:750
1:3
The answer is 1:3