What is the growing speed s of the radius at the moment t

Question

Assume that a disk expands with the speed of area a = 2(cm²/s). Assume that at the moment t = 0, the radius of the disk is 3 (cm). (Recall that the area of a disk of radius R is A=πR²

1) What is the growing speed s of the radius at the moment t? (Your final answer s = s(t) should be a function depending only on t).

2) Use linear approximation to give an approached value of:

s(2.1) = s(2+0.1)