Ok so to find the answer to this you have to make both fractions have the same denominator.
To find the LCD (Least common denominator) follow these steps:
*Think: what number can be divided by both 9 and 5?
The answer is: 45 (shortcut way is to multiply both denominators by each other ie: 9 x 5)
Now make the numerators match:
For -3/5, the denominator (5) is multiplied by 9 to get 45, so the numerator (-3) has to also be multiplied by 9.
You get: -27/45
For 4/9, the denominator (9) is multiplied by 5 to get 45, so the numerator (4) has to also be multiplied by 5.
You get: 20/45
Now the problem looks like this:
-27/45 + 20/45
**Be sure to remember there is a negative sign!
Now we just add the numerators:
-27 + 20 = -7
(If you have trouble doing that remember that you can just subtract the positive number from the negative ie: 27-20 and then just re-add the negative sign)
Then just re-add the denominator:
-7/45
This cannot be simplified so this is the final answer!