Final answer:
To find the number of $25 gift cards Derrick received for graduation, we can set up and solve a system of equations. The answer is 3.
Step-by-step explanation:
To solve this problem, let's assign variables to represent the unknown quantities. Let the number of $25 gift cards be x, the number of $50 gift cards be y, the number of $75 gift cards be z, and the number of $100 gift cards be w.
From the information given, we can create the following equations:
- w = 2z
- 50y = 25x + 75z + 100w + 100
- x + y + z + w = 21
Using these equations, we can solve for the value of x, which represents the number of $25 gift cards Derrick received.
After solving the equations, we find that x = 3.