Did she make a mistake or is it correct? If she made a mistake where did she mess up at ? And if she has it correct how do you know ?

the linear relationship that represents a variation in direct proportion is the linear function that varies according to the numbers of its domain, for example the cost of producing x number of items can be represented in direct proportion by f (x) = mx + b, where m is the constant of proportionality, x the number of articles produced and b the fixed cost

its four gallons, i took the test and this was right.

step-by-step explanation:

on the dot where it starts for four gallons, that's when it doesn't move up any more.