A force of 20N is applied to a 6.0kg mass over a distance of 10m. If the final speed of the mass is 6.0m/s, the energy lost to friction is?

Work = Force*Distance so W=20*10 = 200. Kinetic Energy is 1/2*mv^2 so .5(6)(6^2) = 108. Both of these are in joules. Without friction the blocks kinetic energy would be 200 joules so the friction loss is 92 joules.