The correct expression to determine the amount of time is 45 times startfraction 4 over 9 endfraction times three-fifths.
Sal has finished = 5/9 of 45 maths problems
So, the remaining number of maths problems = 1 - 5/9
The remaining number of maths problem = (9 - 5)/9
The remaining number of maths problem = 4/9 of 45
Amount of time to solve 1 problem = 3/5 of a minute
Amount of time to solve 4/9 problems = 45×4/9 × 3/5 of a minute.
Hence, 45 times startfraction 4 over 9 endfraction times three-fifths is the correct expression to find the time.
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