Question: I need a clearer understanding of how to solve: Maddison has 5 boxes with 50 marbles in each box. Then she gets 20 marbles from her friend. How many marbles does she have now?
Answer: 
Maddison has 5 x 50 = 250 marbles from her boxes.
So she has a total of 250 + 20 = 270 marbles now.