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:
it should be the negative repirocal of -2 so 1/2
There exist a similar question where b = 68 instead of 6. First, determine the measure of the third angle, angle C,
m∠c = 180 - (55° + 44°) = 81°
Let x be the side AB, that which is opposite to angle C. Through the Sine Law,
68 / sin 44° = x / sin 81°
From the equation, the value of x is equal to 96.68. Thus, the answer is letter B.
3.5, it is the coefficient and describes how many n there are
In order to fully understand the problem, it is best to sketch it. Sketching the system, we will see that the system forms a triangle where the angle of elevation is 36 degrees. We are asked to find the hypotenuse. We can use a trigonometric function. It should be noted that one of the sides should also be given in order to calculate the hypotenuse. Trigonometric functions that can be used are:
sin(theta) = opposite / hypotenuse
cos(theta) = adjacent / hypotenuse