Answer :

To reduce a fraction fully, divide the denominator and numerator by their greatest common factor.

Factors of 99: 1, 3, 9, 11, 33, 99
Factors of 143: 1, 11, 13, 143
Common Factors: 1, 11
Great Common Factor: 11

[tex] \frac{99}{11}=9 \\ \\ \frac{143}{11}=13 \\ \\ \frac{99}{143} = \frac{9}{13} [/tex]
[tex]99|3\\33|3\\11|11\\.\ 1|\\99=3\times3\times\fbox{11}\\\\143|11\\.\ 13|13\\.\ \ 1|\\143=\fbox{11}\times13\\\\therefore:\frac{99}{143}=\frac{3\times3\times\fbox{11}}{13\times\fbox{11}}=\frac{3\times3}{13}=\boxed{\boxed{\frac{9}{13}}}[/tex]