Answer:
16 in. X 20 in will keep more.
Explanation:
Length of picture = 4 inches
Breadth of picture = 6 inches
Area of picture=

=

=

Length of frame 1 = 16 inches
Breadth of frame 1 = 20 inches
Area of frame 1 =

So, % of picture can fit in frame 1=

=

=

Length of frame 2 = 18 inches
Breadth of frame 2 = 24 inches
Area of frame 2 =

So, % of picture can fit in frame 2 =

=

=

Since % of picture can fit in frame 1 is more than frame 2 .
So, 16 in. X 20 in will keep more.