A: Yes because for each x value, there is only one corresponding y value.
B: For the first relation, y is half of x, so f(x)=x/2. If x is 8, y is 4.
Plug in the value of x for the second function. 3(8)-10=24-10=14.
The second relation has a greater value.
C: 80=3x-10,
90=3x
x=30