A 1.98 kg mass is set on a spring, and the spring compression an amount 4.78 cm. what is the spring constant?

Well, the spring constant is measured using the F=k∆x, where F is the force, k is the constant, and ∆x is the change in position. So if the mass is 1.98, the force (mxg) is 19.4. Thus the spring constant is 19.4/.0478 (change in position). This equals 405.86.