Determine which relation is a function

What is the value of the digit 1 in the number 13?

Let w=23 . what is the value of w + 45 ?

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