In the first question you have to add the width of bookcase A, B, and C, you will get 334. Now you want to subtract 456 - 334 = 122. 122 is how much space is left, since bookcase D and E are the same width just divide 122 by 2 which is 61. So bookcase D and E have a width of 61 centimeters.
In the second question the height is 1.99 ft. If you multiply 1.99 with 1.33 and 4 you will get 10.66.
I don't know the third question sorry