There is a 10 people(x1,x2,x3,x4,x5...x10) need to line up single file.
a) How many ways can they be lined up it x1 and x2 must stand next to each other(in any order) or x2 and x3 must stand next to each other(in any order)?
b)How many ways can they be lined up it x1 and x2 must stand next to each other(in any order) or x2 and x3 must stand next to each other(in any order) or x4 and x5 must stand next to each other(consecutively)?