15-17. A Math book is 3.78 centimeters thick and an English book is 3.90 cm. thick. How thick will 21 Math books and 15 English books on a shelf.
21, 3.78cm math books would be 79.38 cm, and
15, 3.90cm English Books would be 58.50/58.5cm, all in all it would be 137.80 cm