i did it like this:
3v+14b = v*b
rearrange to vb-3v=14b
v(b-3)=14b
v = 14b/(b-3) b<15 & b cannot be 0 & b is positive integer.
list out possible values of b-3 = 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1
are any of these divisors of 14? 7, 2, 1 are divisors of 14
list values for b for these cases: 10, 5 or 4 hence v = 20, 35 or 56 hence v+b = 30, 40 or 60 ruling out options A, D & E
now checking for cases when b-3 is not divisor of 14 hence it is divisor of b to get integer value for v
possible such values of b-3: 11, 10, 9, 8, 7, 6, 5, 4, 3 hence b = 14, 13, 12, 11, 10, 9, 8, 7, 6
how many of these cases are such that b-3 is divisor of b? 3 is divisor of 6, b=6 hence v = 28, v+b = 28+6=34 rule out B
by process of elimination answer correct:
Canother way to look at it is:b and (b-3) are integers.
any common factor of two numbers has to be a factor of difference between them. b & (b-3) has a difference of 3. so any common factor they share must be factor of 3. 3 only has 1 and itself as factors therefore b & (b-3) cannot share any common factor other than 1 and 3.
14 is prime factorized into 2*7
so (b-3) must have any one or more combinations of prime factors from: {2,7,3}. since the least common multiple (LCM) each of these share is 42, even if all three are present in (b-3), it would still be factor of 42. and any combination of 2,7,3 that (b-3) may be will be factor of 42. thus
(b-3) must be factor of 42 .
v = 14b/(b-3)we know b<15
factors of 42 are : 1,2,3,6,7,14,21,42
check each case:
b-3 = 1 => b=4 => v = 14(4) = 56 => v+b = 56+4 = 60 E is out
b-3 = 2 => b=5 => v=14(5)/2 = 35 => v+b = 35+5 = 40 D is out
b-3 = 3 => b=6 => v=14(6)/3 = 28 => v+b = 28+6 = 34 B is out
b-3 = 6 => b = 9 => v=14(9)/6 = 21 => v+b = 21+8 = 30 A is out
b-3 = 7 => b = 10 => v=14(10)/7=20 => v+b = 20+10 = 30
b-3 = 14 => b = 17 is not valid.
correct answer is C