Answer:
It will take 10 days
Step-by-step explanation:
Here, we want to know the number of days it will take for Bernardo to clear the debt he owes his father.
We proceed as follows;
Let the number of days be x
So after x days, there will be an interest of x * 1 = $90
So the amount of money he owes his father after x days will be $(90 + x)
After x days, the amount he would have earned from mowing lawns will be x * 20 = $20x
He intend using half of this to clear the loan
Half of this is 20x/2 = $10x
We know that this amount is enough to clear the loan, so we equate this value to the amount he wants to use to clear the loan
So;
90 + x = 10x
90 = 10x - x
9x = 90
x = 90/9
x = 10