Kati observes a force of 15 Newtons stretch a spring a distance of 0.450m. a) what is the elasticity coefficient of the spring and b) how much force must be done to stretch the spring a distance of 0.750m?

a) F=Kx
15=K(0.450)
15/0.450=k
33N=k

It seems off to me know sure if done this correct

b) F=15*0.750
F=11N

please help