When it says y varies directly with x it just means that y and x are proportional/equal to each other. The constant of variation and the constant of proportionality are the same thing just different way of saying it so they can confuse you and make your life miserable. Since y and x are proportional to each other and the constant of proportionalty is -5 to make an equation that represents a line you use the formula y=mx+b. That is the slope of the line. With that formula let's first plus in the x so we have y=m2+b. The formula for direct variation is y=kx as well that's good to know and it's good to memorize all these formulas. Math becaomes easier when you have the process down pat and you just need to plug numbers into different equations, expressions, and scenarios. Do m = [y1 - y2] / [x1 - x2] and you'll get the answer.
I believe the answer is 25. Twenty-five is perfectly divisible by 5 If you divide it by 2,3, or 4 there is one left over. So twenty-five is a reasonable answer
