Exercise 4.1: Multidimensional Dot Products
Given: two three_dimensional arrays, x and y, of equal size and range;
Compose: a loop that returns an array of dot (or inner) product of each pair of corresponding rows.
for x_row in x dot y_row in y
returns array of for i in 1, row_size
returns value of sum x_row[i] * y_row[i]