How can i state whether each graphs represents a function? ​

An an average person has 6×10 by the power of two as many red blood cells as white blood cells a small sample of the blood has 7×10 by the power of three white blood cells about how many red blood cells are in the sample

In the polynomial below, what number should replace the question mark to produce a difference of squares? x2 + ? x - 36

Is the square root of 4 plus the square root of 16 rational?