Using the graph, we go up from the x-axis value of 270 to the point where we cut the line. From the point of intersection, we check the value on the y-axis. This turns out to be 20 mmol of calcium carbonate per meter squared per day.
Next, we may determine the time taken for 30 mmol of calcium carbonate to be deposited using:
deposition = rate * area * time
30 = 20 * 1 * time
time = 1.5 days
It will take 1.5 days for 30 mmol of calcium carbonate to be deposited at the given rate.