From the problem, the initial amount of gas in the tank is 25 gallons.
The pump is filling the tank at a rate of 36 gallons per minute.
We can express this as :
where y is the amount of gas after x minutes.
25 is the initial amount of gas
36 is the rate
and
x is the time in minutes.
Rewriting the equation in slope-intercept form : y = mx + b
The answer is
y = 36x + 25