Question

log7(1 - x) = 3
with 7 being the base of the log

Answer 1

(1- x) = 7^3

Answer 2

We have
\[\log_7 (1-x)=3\]
Raise both sides by power of 7
we get
\[7^{\log_7 (1-x)}=7^3\]
we know
\[a^{\log_a x}=x\]
so
\[1-x=7^3\]
I think you can solve now!!