Multiply: (a − 1) by

To multiply, we will use distributive law as follows:b

$(a-1)\left(0.1 a^{2}+3\right)$

$=0.1 a^{2}(a-1)+3(a-1)$

$=0.1 a^{3}-0.1 a^{2}+3 a-3$

Thus, the answer is $0.1 a^{3}-0.1 a^{2}+3 a-3$.