1. **Problem:** Write an equation that represents the total cost $y$ for $x$ GB of data given a fixed fee of 10 plus 3 per GB. 2. **Formula:** The total cost $y$ can be expressed as a linear equation: $$y = mx + c$$ where $m$ is the cost per GB and $c$ is the fixed fee. 3. **Identify values:** Here, $m = 3$ (cost per GB) and $c = 10$ (fixed fee). 4. **Write the equation:** Substitute values into the formula: $$y = 3x + 10$$ 5. **Explanation:** This means for every gigabyte $x$ used, you pay 3 units plus a fixed 10 units monthly fee. **Final answer:** $$y = 3x + 10$$