Answer:
2 weeks.
Step-by-step explanation:
We can solve this problem by just using the given graph.
Notice that the straight line starts at [tex]y=10[/tex], that means in week zero the beard was 10 millimeters long.
First, let's find the constant ratio of change, using two points (0,10) and (20,60)
[tex]r=\frac{60-10}{20-0}=\frac{50}{20}=\frac{5}{2} =2.5[/tex]
According to the ratio, every 5 millimeter grows each 2 weeks, in other words, the ratio of growth is 2.5 millimeters per week.
Therefore, the right answer is 2 weeks.