we have
[tex]f(x)=10-2x[/tex]
we know that
[tex]f(7)[/tex] ----> is the value of the function for [tex]x=7[/tex]
so
substitute the value of x in the function
[tex]f(7)=10-2*7=-4[/tex]
therefore
the answer is
[tex]f(7)=-4[/tex]
