Answer: Supergirl = 19 and Wonder Woman = 8
Step-by-step explanation:
Let g represent the quantity of Supergirl keychains and w represent the quantity of Wonder Woman keychains.
               Qty    Cost
Supergirl         g     $3g
Wonder Woman   w    $2w
Total            27    $73
Qty:   g +  w  = 27  →  -2(g +  w  = 27)   →   -2g - 2w = -54
Cost: 3g + 2w = 73  →   1(3g + 2w = 73)  →   3g + 2w =  73
                                      g      =  19
Input g = 19 into one of the original equations to solve for w:
 g  + w = 27
(19) + w = 27
     w = 8
