I need some help with this question

The value √10 and √15 are plotted on the number line

Kapil needed to buy a long wooden beam. he went to two sawmills that each charge an initial fee plus an additional fee for each meter of wood. the following equation gives the price (in dollars) of a wooden beam from the first sawmill as a function of its length (in meters). p = 5+20xp=5+20x

The roots of the function f(x) = x2 – 2x – 3 are shown. what is the missing number?