f(x,y)=8x+y
This means, f is a function where we plug in pairs of numbers.
then, f calculates the first number times 8, to which it then adds the second number we plugged.
let's calculate f for the vertices:
f(0,0)=8*0+0=0+0=0
f(4, 0)=8*4+0=32+0=32
f(3, 5)=8*3+5=24+5=29
f(0, 5)=8*0+5=0+5=5
the maximum value of f is 32
the minimum value of f is 0
