The fraction 3/4 can also be written as 0.75. The fraction 1/5 can be written as 0.2. So, we can find the unit rate of the time Saul spends studying French to the time he spends studying Spanish by dividing 0.2 from 0.75.
0.75 ÷ 0.2 = 3.75
So, the unit rate of the time Saul spends studying French to the time he spends studying Spanish is hours.
The minus implies that the investment must occur in the first account, not the second. It wouldn't make sense to add more money into the second account, because the second account already exceeds the $188 interest with the amount it has in there. Therefore $1000 must be added from the second account and invested into the first.