Broken motor mount

I recently washed my car and sprayed down the engine. when i started my car and shifted into drive to move it (automatic) there was a loud THUD as my motor smacked the bottom of my hood, i have broken a motor mount, front i think, its ok-ish if i let it run for about ten minutes and roll a little b4 i shift but other wise it lurches and makes a loud noise. what is the method for checking/replacing the mounts front and rear and what is the chance of breaking one and cracking the other? i already have a parts yard Nissan Only Werckers of rancho cardova for parts, i just need a good estimate for both mounts and advice on best mothod of replacement. Thanks