we are given
[tex] 10-10^x=9.9 [/tex]
we can move 10 on right side
[tex] -10^x=9.9-10 [/tex]
[tex] -10^x=-0.1 [/tex]
we cancel -1
[tex] 10^x=0.1 [/tex]
we can rewrite right side
[tex] 10^x=10^{-1} [/tex]
we can compare exponents
and we get
[tex] x=-1 [/tex].............Answer
