6 different sketches each in 2 quantity is required.
Explanation:
Given:
Marta has $50
She wants to display 4 sketches in each row
Number of row is 3
Total number of sketches = 3 X 4
= 12
Since, Marta wants to include each type of sketch at least two times in her array, the number of sketches of each type would be 12/2 = 6
Therefore, 6 different sketches each in 2 quantity is required.