a : 6 = 15 rest 0
a = 15 × 6 + 0
a = 90 + 0
a = 90
b : 6 = 15 rest 1
b = 15 × 6 + 1
b = 90 + 1
b = 91
c : 6 = 15 rest 2
c = 15 × 6 + 2
c = 90 + 2
c = 92
d : 6 = 15 rest 3
d = 15 × 6 + 3
d = 90 + 3
d = 98
e : 6 = 15 rest 4
e = 15 × 6 + 4
e = 90 + 4
e = 94
f : 6 = 15 rest 5
f = 15 × 6 + 5
f = 90 + 5
f = 95