x, a trained and licensed plumber, carelessly installed a stream heater in y"s restaurant and as a result, y was derioluy burned when a heaterpipe exploded z, a qualified medical practitioner who treated y at the hospital ,prescribed an improper medication as treatment for the burn . it aggravated the injury. This obliged y to undergo an expensive skin-graft operation to correct the condition . Discuss the liability of x and z to y