Answer:
2 pills of brand X, 2 pills of brand Y and 3 pills of brand Z.
Step-by-step explanation:
Required Vitamin :
Vitamin A ⇒ 22 unit
Vitamin D ⇒ 18 unit
Vitamin E ⇒ 11 unit
Units of A, Â D, Â E per brand :
X Â Â Â Â Â Â 2 Â Â 1 Â Â 2
Y Â Â Â Â Â Â 3 Â Â 2 Â Â 2
Z Â Â Â Â Â Â 4 Â Â 4 Â Â 1
Let 'u' units of X
   'v' units of Y
   'w' units of Z required
Then,
   2u + 3v + 4w  = 22 ------(1)
   1u  + 2v + 4w  = 18 ------(2)
   2u  + 2v + 1w  = 11 -------(3)
By solving the linear equation
u = 2, v = 2, w = 3
2 pills of brand X, 2 pills of brand Y and 3 pills of brand Z.