Ok, you've got a lot of simplification to do. Order of operations says "please excuse my dear aunt sally", aka parenthesis, exponents, multiplication, division, addition, then subtraction.
Parenthesis first:
Since (3^4) is in parenthesis, you do it first.
3^4 = 3*3*3*3 = 81
So now you have [tex]\frac{7^7 -81^3}{21^9}[/tex]
Exponents:
Now simplify all the exponents.
7^7 = 7*7*7*7*7*7*7 = 823,543
81^3 = 81*81*81 = 531,441
21^9 = 21*21*21*21*21*21*21*21*21 = 794,280,046,581
So now you have 823,543 - 531,441 / 794,280,046,581
Since you can't divide without first subtracting, do that now.
823,543 - 531,441 = 292,102
So now you have 292,102 / 794,280,046,581 = 3.6775694 [tex]* 10^-7[/tex]
Hope this helps =)
