(a) The GST amount included in the invoice is $100.

(b) The GST-exclusive price is $1,000.

**Working**  
Total inclusive amount = $1,100  
GST rate = 10% (1/11 of inclusive total)  
GST = 1,100 ÷ 11 = 100  
Exclusive price = 1,100 − 100 = 1,000  
(Alternatively: 1,100 ÷ 1.1 = 1,000)