You can use Heron's formula: Area = sqrt( s · (s - a) · (s - b) · (s - c) )
where a, b, and c are the sides
and s is the semiperimeter = (a + b + c) / 2.
s = (5 + 7 + 8) / 2 = 10
Area = sqrt( 10 · (10 - 5) · (10 - 7) · (10 - 8) )
And you can finish ...
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