How fast do icicles grow? We have data on the growth of icicles starting at length 10 centimeters (cm) and at length 20 cm. Suppose that icicles which start at 10 cm grow at a rate of 0.15 cm per minute and icicles which start at 20 cm grow at the same rate, 0.15 cm per minute. Give a regression model that describes how mean length changes with time x1 and starting length x2. Use numbers, not symbols, for the β’s in your model.