Answer:
There are 45 library books in the classroom.
Step-by-step explanation:
The problem says that Marvin, Latoya and Abdulla each read 3/7 of the library books in the classroom. If Latoya read 3/7 of the books, we can form a proportion to determine the number of total library books in the classroom.

To solve for 'x', we can either cross-multiply and divide, or we can multiply the denominator by the same factor as the numerator to get a product of 15. In this case, the same factor would be 5, so 7 x 5 = 35. If we cross-multiply:
3x = (15)(7) or x = 35.
Sin = opposite / hypotenuse
cos = adjacent / hypotenuse
using pythagoras theorem =
adjacent = 5^2-3^2
= 16
= square root 16
=4
cos x = 4/5