Question 739230
Your description does not indicate multiplying exponents.


You said, converted into symbols, {{{7^8*7^(-1)*7^(-5)}}}.  The only base for the exponents is 7.


The formal rule you could use, if you want it, is, for real number {{{b<>0}}}, 
{{{b^m*b^n=b^(m+n)}}}.