From the definition of logarithm, we know that:

In this case

and

so:
Answer:
140 = 40 + 10x
Step-by-step explanation:
The watch is 140 in total. He can pay 40 dollars currently. 10x is the amount of payments there are. How much he can pay with each payment (10x) is unknown so that is why there is the variable.
Y=3 because it is horizantal line that is between 0 and 6
(74 + 78 + 70 + x) / 4 = 80
Divide each number by 4.
18.5 + 19.5 + 17.5 + x = 80
Add the numbers you know so far.
18.5 + 19.5 + 17.5 = 55.5
You need 24.5.
Now, since we divided all the others by 4, we have to multiply 24.5 by 4 to see what the exam score would be.
24.5 * 4 = 98.
To get an average of 80%, the student would need to get a 98 on their fourth exam.