Which graph is the result of reflecting f(x) = (8)x across the y-axis and then across the x-axis?

Assuming yo mean f(x)=8ˣ

to reflect the function across the y axis, multiply every x by -1
to reflect the function across x axis, multiply the whole function by -1

see attachment for graphs
red=original line

so across y axis would be

f(x)=(8)⁻ˣ
this is the blue line

reflection across x axis then would be
f(x)=-1(8)⁻ˣ
this is the green line

so the resulting graph is the green line

Check the picture below.