Answer: 21
Step-by-step explanation: To solve this problem, we can first set up a proportion because we know that 3 is to 7 as 9 is to x.
So we have
.
Now, we can use cross products to find the missing value.
So we have 3 time x which is 3x and 7 times 9 which is 63.
Rewriting our equation, we have 3x = 63.
Dividing both sides by 3, we find that x = 21.
So, x = 21.
The red arrows in the middle mean that they are parallel so the slopes are the same.