Answer :
As per given by the question,
There are given that a original form is,
[tex]4(a-1)+3=15[/tex]Now,
The first step of the given equation is,
[tex]\begin{gathered} 4(a-1)+3=15 \\ 4a-4+3=15 \end{gathered}[/tex]Then,
The value of the given equation is,
[tex]\begin{gathered} 4a-1=15 \\ 4a=15+1 \\ 4a=16 \end{gathered}[/tex]So, here distributive properties used by the student to solving the first step.
Hence, the first step is 4a-4+3=15.