6. Use K-maps to simplify the following four variable Boolean expressions expressed in the Sum of Minterms notation (15 points). a. b. C. f(w,x,y,z)=(0,1,4,5,10,11,14,15) f(w,x,y,z)=(5,7,9,11,13,15) f(w,x,y,z)=(2,3,6,7,8,10,13,15)