The first step is to solve the integral:
#int1/x^(4/3)dx# really is #int# #x^-(4/3)dx#
#int# #x^-(4/3)dx ->-3/(root(3)(x))+"c"#
Knowing this we can proceed:
#int_5^oo 1/x^(4/3) dx# is equal to what is below
#lim_{b to oo}-3/(root(3)(x))# Evaluated from #5# to #b#
#lim_{b to oo}[-3/(root(3)(b))-(-3/(root(3)(5)))]#
#lim_{b to oo}[-3/(root(3)(b))+3/(root(3)(5))]#
When we take the limit of:
#lim_{b to oo}[-3/(root(3)(b))]# We get #-3/oo# Anything over infinite is zero.
#[-3/(root(3)(oo))+3/(root(3)(5))]#
The answer should look like this once you take the limit of course you can disregard the zero:
#[0+3/(root(3)(5))]#