Answer :
[tex]\begin{gathered} \text{The first number is x,} \\ The\text{Second number is }\Rightarrow x+15 \\ \text{Now, } \\ x+x+15=91 \\ 2x=91-15 \\ 2x=76 \\ x=38(\text{smaller number)} \\ Bigger\text{ number}\Rightarrow38+15=53 \end{gathered}[/tex]