In step 1, Megan attempts to equate the amount of cake per person. She swapped the first fraction. There she should have divided 2 cakes over 75 people, ie., 2/75. Then step 2 would have been:
Step 2: (2)(150) = 75x
Step 3: 300 = 75x
Step 4: x = 300/75 = 4