If m and n are positive integers, what is the value of 3/m + n/4 ?

\(\frac{3}{m} + \frac{n}{4} =\frac{12+mn}{4n}\)

(1) mn = 12
If m=3 and n=4....\(\frac{12+mn}{4n}=\frac{12+12}{4*4}=\frac{3}{2}\)
If m=1 and n=12....\(\frac{12+mn}{4n}=\frac{12+12}{4*12}=\frac{1}{2}\)
Insufficient

(2) 3/m is in lowest terms and n/4 is in lowest terms.
This means that m is NOT a multiple of 3 and n is NOT a multiple of 2 .
We know nothing about m and n.
m and n could be 4 and 3 OR 7 and 7..
answer will be different
Insufficient

Combined..
mn=12=1*12=2*6=3*4..
m and n can be 1 and 12 or 12 and 1 ...NO, m can NOT be a multiple of 3 and n can NOT be a multiple of 2 ...
m and n can be 2 and 6 or 6 and 2.......NO, n cannot be a multiple of 2
m and n cannot be 3 and 4 ...NO, m can NOT be a multiple of 3 and n can NOT be a multiple of 2 ...
So, ONLY possibility is m and n can be 4 and 3...
m=4 and n=3....\(\frac{12+mn}{4n}=\frac{12+12}{4*3}=2\)
Sufficient

B
_________________

when it is a multiple, the fraction wont be in its lowest term e.g . 3/12,3/9,3/6..... is not in its lowest term right? why? because 12 is a multiple of 3 and 9,6 are all multiples of 3.
lowest term for 3/12= 1/4 , 3/9=1/3 ...etc

now 3/7 ,3/8,3/5,3/13.......is in its lowest term right? why? because seven (7) aint a multiple if three (3) , we can also say 3 and 7 ,3 and 8 ........are co-prime
got it?