Let a,b & c be the number of cookies Adrian, Bobby and Calvin baked respectively.
(a+b+c)/3 =138
(a+b)/2 =136
a+b=272
a=272-b
(b+c)/2 =125
b+c=250
c=250-b
Sub a=272-b and c=250-b into (a+b+c)/3 =138,
(a+b+c)/3 =138
[(272-b)+b+(250-b)]/3 = 138
272-b+b+250-b = 414
-b = -108
b=108
From the above,
a=272-b
=272-108
a=164
c=250-b
=250-108
c=142
∵ a=164
b=108
c=142
∴ Adrian baked 164 cookies.
Bobby baked 108 cookies.
Calvin baked 142 cookies.