Converting to base 10 can be done easily by writing a sort of digit expansion. In base 6, this number literally means
[tex]13542_6=1\times6^4+3\times6^3+5\times6^2+4\times6^1+2\times6^0[/tex]
Simplifying this gives the value in base 10.
[tex]13542_6=1296+3\times216+5\times36+4\times6+2[/tex]
[tex]13542_6=2150_{10}[/tex]