Explanation:
y = ax + b
I see already the result (y = x/10 × 1/6), but let's go in formally.
we have multiple function points to use to officially calculate a and b.
1/6 = a×10 + b
2/3 = a×40 + b
5/6 = a×50 + b
1 2/3 = a×100 + b
let's e.g subtract equation 1 from equation 3.
4/6 = a×40 + 0
a = 4/40 / 6 = 4 / 240 = 1/60
1/6 = 10/60 + b
1/6 = 1/6 + b
b = 0
so, the function is
y = x/60
x = 25
y = 25/60 = 5/12 cups