The process is:
C = 2nr
2nr = c
r (2n) = c

That's the answer☝️☝️☝️☝️
or maybe this one
r = 2n + c
sorry, I'm unsure, it has been too long since I studied that...
Answer:
n + 6(3/10)
Step-by-step explanation:
6(3/10) is written as a mixed number
#27.
First cross multiply
2 (2a-3) = 3 (a-1)
next use the distribute property on both sides
4a - 6 = 3a - 3
combine like terms, subtract 3a from both sides and add 6 to both sides
a = 3
#28
cross multiply
3x = 4, then divide both sides by 3
x = 4/3
#30
add 1/4 to both sides
3/x = 1/2 + 1/4, find a common denominator for the right side fractions
3/x = 2/4 + 1/4 = 3/4
therefore, x = 4
Answer: 60 of the patients are boys.
Step-by-step explanation: According to what is described, 5 in 8 patients are girls, then: 8 - 5 = 3, i.e., 3 in 8 are boys.
Mathematically the proportionality is 
If 160 patients have appointments per month and
are boys:
160.
= 60
Per month, 60 boys have appointments at the medical office.
So,
9*27 + 2*31 - 28 = n
We use PEMDAS.
Multiply from left to right.
243 + 2*31 - 28 = n
243 + 62 - 28 = n
Add or subtract from left to right.
305 - 28 = n
277 = n