Answer:
a. 140 N/cm
Step-by-step explanation:
The relationship between force applied, spring constant and compression/stretching of a spring is

where
F is the force applied
k is the spring constant
x is the compression/stretching
In this problem, we have:
x = 0.250 m is the compression
F = 35 N is the force applied
Substituting and re-arranging the equation, we find the spring constant:
