Question

11-(7*5-9*9:f:3):8=7

Answer 1

11-(35-81:f:3):8=7
(35-81:f:3):8=4
35-81:f:3=32
81:f:3=3
81:f=9
f=9

Answer 2

$11-(35-81:f:3):8=7$
$(35-81:f:3)=11-7$
$(35-81:f:3):8=4$
$(35-81:f:3)=8*4$
$35-81:f:3=32$
$81:f:3=35-32$
$81:f:3=3$
$81=3*3$
$81:f=9$
$f=81:9$
$f=9$