A collection of four types of industrial shims, designated S1, S2, S3, and S4, have precise thicknesses of 1.10 mm, 1.60 mm, 2.10 mm, and 2.60 mm, respectively. If a stack formed by these shims measures exactly 20 mm in total height, what is the total number of shims in the stack?
8
9
10
11
12
