Hey , wondering if anyone could help me with this problem:

What was the rate, in km^2/yr, that each of the glaciers receeded between 1850 and 1993?

a. Aggasiz Glacier

b. Vulture Glacier

The values for them are:

1850 Area:

a. Aggasiz 4.06 km^2

b. Vulture 0.77 km^2

1993 Area:

a. Aggasiz 1.02 km^2

b. Vulture 0.21 km^2

I need to find the speed, not the percentage (which I figured out in a previous question which was 75% and 73% respectively).

I did this question, but I forgot how to get the answers. They are:

a. 0.0214 km^2/yr

b. 0.00392 km^2/yr