10C4 represent the Combinations of 10 objects taken 4 at a time.
The formula for nCr is:

In the given case, n=10 and r=4. Using these values we get:

This means we can make 210 combinations of 10 objects taken 4 at a time.
Answer:
Use area of trap formula and special right triangles
Step-by-step explanation:
A = (.5)(10 + 18)(5)
Find 2% of 7 billion.
7,000,000,000 x .02 = 140,000,000
About 140 million people have red hair.
If you were going to multiply those two numbers, the answer would be D, 192.