Learning equity distribution through riddles

You don't need a lot of accounting to solve this riddle. First, recognize that the time period in which all these investments are happening is one year (12 months). Andrew starts the business with a monthly capital contributions of $3500. Thus, his total contributed capital (the amount of his own money he puts into the business) = $3500 x 12 = $42000.

After 5 months, Brenda is accepted as a partner. She makes monthly capital contributions as well, but she has only 7 months in which to make contributions. Her monthly contributions are X, and her total contributed capital is 7X.

Finally, the split the profits in a 2:3 ratio. Each person has a right to a percentage of the profit equal to the amount of capital they contributed to the business. Since the ratio of Andrew:Brenda is 2:3, Brenda's total contribution to the business is 3/2 of Andrew's.

Brenda's yearly contribution = 7X = 3/2*(Andrew's yearly contribution) = 3/2*(42000) = $9000/month.