5(a + 3b) = 5(9 + 3(2)) = 5(9 + 6) = 5(15) = 75
X=5 because you add 2 to both side and get 3x=15, and then you divide both sides by 3 to get x alone, and get 15/3 which equals 5
Anything without a variable in front.
In other words, the constants are -3.7 and 1/3
It would take 10.7 years.
The formula for continuously compounded interest is:

where P is the principal, r is the interest rate as a decimal number, and t is the number of years.
Using our information we have:

We want to know when it will double the principal; therefore we substitute 2P for A and solve for t:

Divide both sides by P:

Take the natural log, ln, of each side to "undo" e:

Divide both sides by 0.065:
He starts on the 1st floor. He then goes up 18 floors:
1 + 18 = 19
He took the stairwell down 3 floors
19 - 3 = 16
He then takes the elevator down 8 floors
16 - 8 = 8
He then takes the stairwell up 5 floors for his afternoon meeting
8 + 5 = 13
C. thirteenth is your answer
hope this helps