Answer:
[tex]A\approx43.2\:\text{m}^2[/tex]
Step-by-step explanation:
Find the missing side using Pythagoras' Theorem
[tex]a^2+b^2=c^2\\5^2+b^2=18^2\\25+b^2=324\\b^2=299\\b=\sqrt{299}\:\text{m}[/tex]
Find the area of the triangle
[tex]\displaystyle A=\frac{bh}{2}\\ \\A=\frac{5\sqrt{299}}{2}\\ \\A\approx43.2\:\text{m}^2[/tex]
