Ok so we can see for every 2 cups of medium coffee, the balance goes down 5.30$. So that means that for every coffee, her balance goes down 2.65$. Solving for the x-intercept means how many medium coffees can I get until my balance is 0. First, we have to find the y-int so it's easy. The slope is -2.65 because for every medium coffee, her balance goes down 2.65$. So we have y=-2.65x+b. Plugging in any point, I choose (4,14.40), we get 14.4 = -2.65 × 4 +b. Solving for b we get 25 for the y intercept, meaning the equation is y = -2.65x + 25 . To find the x intercept, we set y=0. So we have 0 = -2.65x+25. Solving for x we get approx. 9.4. We can't have decimals so we round down to 9. So the x int is ≈ 9.4 meaning we can only buy 9 coffee and have a little extra. But, if the problem said how many more coffees can she get, then here is how we do it. Since she already got 4 coffees, and the max is 9, we do 9-4 and we get 5, so she can buy 5 coffeed more.
