A F a Force Of $10 \mathrm {~N}$ Causes a Spring to Stretch

A f A force of $10 \mathrm {~N}$ causes a spring to stretch $50 \mathrm {~cm}$ . What is the spring constant?
a. $500 \mathrm {~N} ^ { \cdot } \mathrm { cm }$
b. $0.2 \mathrm {~N} / \mathrm { m }$
c. $5 \mathrm {~cm} / \mathrm { N }$
d. $20 \mathrm {~N} / \mathrm { m }$