The formula for circumference is

.
To express the circumference exactly, plug the diameter in for

and put the

symbol in front of it. Don't multiply. This expresses the exact circumference.
Say you have the diameter of 17.
You can express the circumference with 17

.
Answer:

Step-by-step explanation:
The function is given.

To find : 
The input for the function f(x) is (a + 1).
Replace x with (a + 1).

Expand brackets.

Simplifying.

Answer:

Hope this helps.
Step-by-step explanation:
Correct Question:
John works as a tutor for $12 an hour and as a waiter for $8 an hour. This month, he worked a combined total of 86 hours at his two jobs.
Let be the number of hours John worked as a tutor this month. Write an expression for the combined total dollar amount he earned this month.
Answer:
Total hours = 86
Let t is the hours he spent on tutoring
then (86-t) is hours spent on waiting
Let Y is the total amount in dollars which is required .
Now;
y = (tutoring hours x 12$) + (waiting hours x 8$)
Y = 12t + 8(86-t)
Let x = amount of 70% juice we use.
Then 60-x = amount of 85% juice we'll use.
We'll set up an equation that is based on how much pure juice comes from each component and how much we need in the final mixture.
So 70% of x plus 85% of (60-x) must equal 80% of 60, or...
0.7x + 0.85(60-x) = 0.8(60)
0.7x + 51 - 0.85x = 48
-0.15x + 51 = 48
-0.15x = -3
x = 20
Then 60 - x = 60 - 20 = 40
Check: 70% of 20 pints = 14 pints of pure juice.
85% of 40 pints = 34 pints of pure juice
That's 48 pints of pure juice in the mix, which matche 80% 0f 60 pints.
You'd need 20 pints of the 70% juice and 40 pints of the 85% juice.