To simplify the exponent you have to remember the following rule:
When you have the following expression:
[tex](a^b)^c[/tex]To simplyfy it you have to multiply both exponents:
[tex](a^b)^c=a^{b\cdot c}[/tex]In this exercise is:
[tex](6^3)^5=6^{3\cdot5}=6^{15}[/tex]The simplified expression is then:
[tex]6^{15}[/tex]