How to solve this ? ? they are similar triangles and we need to find the area a

Hello i need some with trigonometric substitutions. [tex]\int\limits^a_b {x} \, dx[/tex]

Tell whether the two rates form a proportion

Huong is organizing paperback and hardback books for her club's used book sale. the number of paperbacks is 12 less than three times the number of hardbacks. huong had 162 paperbacks. how many hardback books were there?