Use the formula KE = (1/2) mv2. (Kinetic energy = 1/2 x mass x speed squared.) Replace the values you know, and solve the resulting equation for the speed.
Kinetic energy is measured in joules. A joule is defined as a ((kilogram)(meter)2)/(second)2. This means that the units for the parts of the equation need to multiply to be a kilogram meter squared...