Mu Aung spends all her income on two goods: pens and paper. Her income is $100, the price of paper is $10 a pack, and the price of pens is $2. Put paper on the horizontal axis and put pens on the vertical axis. The horizontal intercept for Mu Aung's budget line is equal to ______ units of paper. Select one: a. 5 b. 100 c. 50 d. 10