Answer:
?=7
Step-by-step explanation:
Here is a cool trick that I believe only works with 9.
Add the numbers, 3+9+9+8+x= divisible by 9.
3+9+9+7+8 is 36 which is the only number divisible by 9.

It was started by a scientist Ivan Pavlov who was a russian physiologist who started the Behaviorist movement in psychology.
During the experiment:
- The loud noise is the <u>unconditioned stimulus.</u>
- The fear reaction is the <u>unconditioned response.</u>
- The white rat is our <u>neutral stimulus.</u>
- When the loud noise and the white rat are paired over time, the white rat becomes the <u>conditioned stimulus.</u>
- The Fear reaction to the loud noise the <u>conditioned response.</u>
Our Answer is:
⛱️ 
-89/40. First, u need to make a common denominator. In this case, u should use 40. Multiply he first term by 5, which get u -25/40. Multiply the second term by 8, which gets u -64/40. Now add the 2 negatives: -25/40 + (-64/40) u get -89/40
I’m just here so I could ask a question