How much work must you do to change a springs length from 9 cm to 13 cm?

The spring has a relaxed length of 4 cm and a stiffness of 150 N/m.How much work must you do to change a springs length from 9 cm to 13 cm?
E=(1/2)k*delta_x^2



=(1/2)*(150N/m) * (.04m)^2

=.12Joules