Make sure you add the parts that are like.
You can think of $0.045$ as

$\frac{4}{100}\text{ and } \frac{5}{1000}\text{ or is }\frac{45}{1000}.$

How can you combine this with the other numbers?
Be sure to show your work.

You can think of $56.7$ as $56\frac{7}{10}$  and $0.23$ as  $\frac{23}{100}$.

How can you subtract $23$-hundredths from $70$-hundredths?

$0.234$

Since $7.5$ is greater than $6.3$, your answer should be less than zero.

$−1.2$