Solve the following arithmetic problems: 15. -48 / 6 = ?, 16. -5 -3 2 = ?, 17. -20 - 15 + 10 = ?, 18. -8 + (-3) - (-12) = ?, 19. A submarine is at -150m and rises 80m. What is its new position? 20. Co

$$
15 \times 2 = 30
$$
The answer is $\boxed{30}$.

17. Step 1: Perform the first subtraction. $-20 - 15 = -35$

$$
-35 + 10 = -25
$$
The answer is $\boxed{-25}$.

18. Step 1: Simplify the expression by changing subtraction of a negative to addition. $-8 + (-3) - (-12) = -8 - 3 + 12$

$$
-11 + 12 = 1
$$
The answer is $\boxed{1}$.

19. Step 1: The initial position is $-150$ metres. Rising 80 metres means adding 80 to the current position. $-150 + 80 = -70$ The new position is $\boxed{-70 \text{ metres}}$.

20. Step 1: Compare $-9$ and $-4$. Since $-9$ is to the left of $-4$ on a number line, it is smaller. $$-9 < -4$$

Since 0 is to the right of $-1$ on a number line, it is larger. $0 > -1$

Since $-15$ is a negative number and 15 is a positive number, $-15$ is smaller. $-15 < 15$ The completed comparisons are: $-9 \boxed{<} -4$ $0 \boxed{>} -1$ $-15 \boxed{<} 15$