Answer
$0.3 \;mg$.
Work Step by Step
Number of tablets $N=3$.
One tablet contains $Q=0.1\;mg$ of clonidine hydrochloride.
Total intake $=N\times Q$
Substitute all values.
Total intake $=3\times 0.1 \;mg$
Simplify.
Total intake $=0.3 \;mg$.