To find area $ A $ use formula:
$$ A = \frac{ (a + b) \cdot h}{ 2 }$$After substituting $ a = 1100 $ , $ b = 1000 $ and $ h = 900 $ we have:
$$ A = \frac{ (1100 + 1000) \cdot 900}{ 2 }$$$$ A = \frac{ 2100 \cdot 900}{ 2 }$$$$ A = \frac{ 1890000 }{ 2 }$$ $$ A = 945000 $$