73,980=70,000+3,000+800+90+0
100=100+00+0
8 thousands is equal to 8000.
15 hundreds is equal to 1500.
15 tens is equal to 150.
18 ones is equal to 18.
So just add them up.
8000 + 1500 = 9500.
9500 + 150 = 9650.
9650 + 18 = 9668.
The number is 9668
Among many other formulas, the area of a triangle is
![S = \frac 1 2 a c \sin B](https://tex.z-dn.net/?f=%20S%20%3D%20%5Cfrac%201%202%20a%20c%20%5Csin%20B%20)
where B is the angle between sides a and c.
![S=\frac 1 2(10)(20) \sin 67^\circ \approx 92.05 \textrm{ sq cm}](https://tex.z-dn.net/?f=%20S%3D%5Cfrac%201%202%2810%29%2820%29%20%5Csin%2067%5E%5Ccirc%20%5Capprox%2092.05%20%5Ctextrm%7B%20sq%20cm%7D)
Answer: 92.05 sq cm, first choice
Bonus. Here's a formula for the area S of a triangle your teacher doesn't know:
![16S^2 = 4a^2b^2 -(c^2-a^2-b^2)^2=(a^2+b^2+c^2)^2-2(a^4+b^4+c^4)](https://tex.z-dn.net/?f=16S%5E2%20%3D%204a%5E2b%5E2%20-%28c%5E2-a%5E2-b%5E2%29%5E2%3D%28a%5E2%2Bb%5E2%2Bc%5E2%29%5E2-2%28a%5E4%2Bb%5E4%2Bc%5E4%29)