what does the number 1 in the equation mean in this context?

Answer:
last option at the bottom.
Step-by-step explanation:
we are told that the the equation
y = 0.73x + 1 represents the Length of the spring when a stretch force is applied,
basically y = length of spring and x = force applied.
from the graph, we can see that when stretch force = 0 (i.e x = 0)
the equation becomes y = 1.
That is to say that the spring has a length of 1 inch when stretch force is zero
(which basically is the same as the last option)