Im not completely sure, because I have to know what S and R mean; however, the equation is basically saying that the amount of money saved= is 450$ and every time he does “R”, he saves another 100$
For this case, the first thing we must do is define variables.
We have then:
x: number of minutes
y: final temperature
We write then the equation that models the problem:

For y = 20 we have:

Clearing x:
Answer:
The temperature of the water will be 20 degree celcius after 150 minutes
Answer:
{2,4} I know cause I JUST took the same test yesterday :) I guess I didin't help much huh