A 500 gallon tank initially contains 100 gallons of fuel oil. A pump is filling at a rate of 4 gallons per min?

How full = Amount already in there + how fast it fills * how long it has been filling for F = how full C = Ammount that is in there r * t = x rate at which it fills, t = time it has been filling. F = rt + C ( per y = mx + c classic linear reference) solve for t, by setting F (or maybe V) for fullness or Volume you want after whatever time = 500 I leave you to complete it (you have to some work eh ?) and change the values for x, and f(x)

since its a linear function, then using this formula: ( f - f 1 ) = m ( x - x 1 ) m: the slope of the linear function or the filling rate ( m = 4 ). x : the time in minutes. f : the number of gallons as a function of x. initially ( time = 0 , x 1 = 0 ) and the number of gallons = 100 = f 1 , so ( f - 100 ) = 4 ( x - 0 ) f = 4 x + 100