Answer
$3$; $second$; $-2$; $third$.
Work Step by Step
Recalling the rules of row operations, we can complete the sentences as:
We can obtain $0$ in the position shaded by a rectangle if we multiply the top row of numbers by $3$ and add these products to the $second$ row of numbers. We can obtain $0$ in the position shaded by an oval if we
multiply the top row of numbers by $-2$ and add these products to the $third$ row of numbers.
