What we know:
Korena is paid $40 every five times she does the job
What we need to figure out:
How many times does she have to do it to earn $100
Math:
First I'm going to figure out how much she makes each time she weeds
Money earned ÷ Amount of times
40 ÷ 5
= 8
In order to determine the rest of the time we are going to multiply everything we know by 2
Korena is paid $80 if she does it 10 times
We clearly aren't going to do that again because that will surpass the amount so now we are going to use the unit rate we figured out;
($8 per time)
Korena is paid $88 if she does it 11 times
Korena is paid $96 if she does it 12 times
Korena is paid $104 if she does it 13 times
Statement
Therefore if Korena weeds the garden 13 times she will make $104 surpassing the $100 needed.