What is the primes number between 1 and 6

What is the name used to describe a graph where for some value of x, there exists 2 or more different values of y?

Pranza plotted point a in the coordinate plane below.

List x1, x2, x3, x4 where xi is the left endpoint of the four equal intervals used to estimate the area under the curve of f(x) between x = 4 and x = 6. a 4, 4.5, 5, 5.5 b 4.5, 5, 5.5, 6 c 4.25, 4.75, 5.25, 5.75 d 4, 4.2, 5.4, 6