I'm not sure exactly what you're trying to ask, but this statement is not true.
to solve a function, you would input a number ,and in this example 8, and replace the x's with 8.
f(8)=4(8)+7
f(8)=32+7
f(8)=39, so when you input 8, your output is 39, not 11.
the function is linear.
