Does the function f(x)=x-7 increase?
( explain, i'm not sure what the question means)

YES
it is increasing ...

why?!?

becasue as the values of x increase ( x=1 then 2 then 7 then 15 ...), the resulting values of y also increase..

Do it yourself to reassure ...

Well, increase could mean it has a positive slope

1 way is to find the slope
y=mx+b
m=slope
so given
f(x)=x-7
y=1x-7
1>0
it is positive so it increasese

the easier way is
if it increases then if x increases then y will increase as well

test some points
if x=1, y=-6
if x=2, y=-5
x increased and y increased
it is an increasing function

The answer to that is 6