In how many ways can six people be arranged in a wedding photo if:

a) the bride and groom must be together
We treat the bride and groom as 1 entity and figure out the ways of arranging 5 things. We then multiply by the number of ways of arranging the bride and groom:
  5*4*3*2*1 * 2 = 240

b) the bride and grrom must be seperate
We already found the number of ways in which the bride and groom are together so this should be easy. We just subtract that from the total number of possible ways to get the answer:
  6*5*4*3*2*1 - 5*4*3*2*1 - 5*4*3*2*1 = 720 - 120 - 120 = 480

c) the bride is positioned somewhere to the left of the groom.
This equal to the total of possible ways for 6 minus all the possible ways to have the bride to the right of the groom.
  6*5*4*3*2*1 - 3*5*4*3*2*1 = 720 - 360 = 360