For each of the first, third and fourth rows, you have 4 + 3 + 2 + 1 = 10 rectangles

For the second row, you have 3 + 2 + 1 = 6 rectangles.

No. of rectangles by combining first row & second row together, second & third row together and third & fourth row together is 3 rectangle

No. of rectangles by combining first, second & third together and second , third & fourth row , you have 2 rectangle.

No. of rectangles by combining all the four rows, you have 1 rectangle

Hence, total rectangles = 3(10) + 6 + 3 +2 +1 = 42.

Hence, Option C. is the answer