Substitute a complete input expression

The Teacher completes the Student blank: $f(3)=3(3)^2+1=28$.

Replace the entire input by $5x$: $f(5x)=3(5x)^2+1=75x^2+1$. Squaring affects the factor 5 as well as x.

The printed stages are $3(2y+1)^2+1=3(4y^2+4y+1)+1=12y^2+12y+4$. Keep the whole input in parentheses before expanding.