Given the general rule for exponents:
[tex]a^n\cdot a^m=a^{n+m}[/tex]then, in this case we have the following:
[tex]\begin{gathered} 100^2x100^5=100^y \\ \Rightarrow(100^2)\cdot(100^5)=100^{2+5}=100^7 \\ \Rightarrow y=7 \end{gathered}[/tex]therefore, y=7
