Question 1113380

What you do for these types of problems is substitute for x.   
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I will do part (c), where we let x=a+2 in f(x):

     f(x) = {{{ 3-x^2 }}} 
    f(a+2) = {{{ 3 - (a+2)^2  = 3 - (a^2+4a+4) =  highlight( -a^2 - 4a - 1 ) }}}

The other two parts will produce numeric answers.