Question 900605
x+x+6+x+12+x+18=444
4x+36=444
4x=408
x=102 the first day

This is an arithmetic progression
S = ½(2*a1 + (n-1)d)n
444 = ½(2*a1 + (3)6)4
a1 = 102

102 the first day 
102+6=108 the second day 
108+6=114 the third day
114+6=120 the 4th day
102+108+114+120=444
x+x+6+x+12+x+18
an = a1 + (n - 1)d

a2 = 102 + (1)6=108
a3 = 102+ (2)6=114
a4 = 102 + (3)6=120