Question 911454

{{{f(x)=5x-4 }}}

{{{f(4a)=80}}} => means {{{x=4a}}}

{{{80=5*4a-4 }}} ...solve for {{{a}}}


{{{80=20a-4 }}}

{{{80+4=20a }}}

{{{84=20a }}}

{{{84/20=a }}}

{{{4.2=a }}}

check:

{{{f(4a)=80}}}

{{{f(4*4.2)=80}}}

{{{f(16.8)=80}}} check that {{{f(16.8)=5x-4 }}} =>{{{f(16.8)=5*16.8-4 }}} =>{{{f(16.8)=84-4 }}}  =>{{{f(16.8)=80 }}}