Can you help me with this...thank you

Answer:
[tex]a=\frac{1}{2}\times \: h(a+b)[/tex]
[tex] \frac{1}{2 } \times 9(18 + 24) [/tex]
24 + 18=42
[tex] = \frac{1}{2} \times 9(42)[/tex]
[tex] \frac{1}{2} \times 378[/tex]
=189cm²
Step-by-step explanation:
just use the formula but I'm not sure if my calculation is correct lol