(a) GST included: **$100**

Working:  
\[
\text{GST} = \frac{1}{11} \times \$1{,}100 = \$100
\]

(b) GST-exclusive price: **$1,000**

Working:  
\[
\$1{,}100 - \$100 = \$1{,}000
\]