A researcher measures a temperature that drops linearly from 90°C at time t = 0 minutes to 70°C at t = 5 minutes. Express temperature T as a function of t using slope-intercept form T = mt + b.

• A. T = -2t + 80
• B. T = 4t + 90
• C. T = -4t + 90
• D. T = -4t - 90

Answer: (C)