she has 4 choices. draw the tree diagram like this:
cheese,tomato
cheese,lettuce
cheese,ham
tomato,cheese
tomato,lettuce
tomato,ham
lettuce,cheese
lettuce,tomato
lettuce,ham
ham,cheese
ham,tomato
ham,lettuce
if you still dont understand look up on google images tree diagram
comment back if you have any questions, im always online
