It is called an equation.
Short Answer: 18 minutes
Remark
The answer to this problem is less than the smallest time of the two people working together. that fact lets out C and D (38 minutes and 75 minutes). Now you have to choose 15 minutes and 18 minutes. There's a method. No guessing needed.
Givens
Let the time for Sophie = S
Let the time for Simon = M
Let the job to completion = 1
S = 45 minutes
M = 30 minutes
Step One
Convert minutes to hours.
45 minutes = 45 / 60 = 3/4 hour = 0.75 hour
30 minutes = 30 / 60 = 1/2 hour = 0.50 hour
Step Two
Set up the Equation
The formula is a form of job / hour.
Let the time = t that they both have to work
job = 1 in these problems.
1/S + 1/M = 1/t
1/0.75 + 1/0.5 = 1/t
Solve
1 ÷ 0.75 = 1.33333
1 ÷ 0.5 = 2
1.3333 + 2 = 3.33333
3.3333 = 1 / t Multlply both sides by t
3.3333*t = 1
t = 1 / 3.333333333
t = 0.3 of an hour
1 hour = 60 minutes
0.3 hours = x Cross Multiply
x = 60 * 0.3
x = 18 minutes
Answer working together it took them 18 minutes <<<<<
well, we know that 213.90 includes the 15% gratuity, so if the meal price was say "x", namely that is the 100%, and we add 15% to that, then 100% + 15% = 115%, so 213.90 is really the 115%.
now, if 213.90 is the 115.%, what is "x"? the 100%.

so since we know the meal without the tip is 186 bucks, the tip was then 213.90 - 186 = 27.90.
but they got extra potato wedges with butter and the waitress was wearing her best hat, they added $20 more, so the tip ended up as 27.90 + 20 = 47.90.
now, if the cost of the meal was $186 and that is the 100%, what is 47.90 off of it in percentage?

I looked it up and it said it was c
Answer:
9
Step-by-step explanation:
45 Cookies... 5hrs
? cookies... 1 hr
45 ÷ 5 = 9
9 cookies per hour