Of the 15-year-olds at a karate school, 9 have black belts and 15 have brown belts. among the 16-year-olds, 11 have black belts and 20 have brown belts. which age group has a higher ratio of black belts to brown belts?

(a) calculate the molarity of a solution that contains 0.0345 mol nh4cl in 400 ml of solution. (b) how many moles of hno3 are present in 35.0 ml of a 2.20 m solution of nitric acid? (c) how many milliliters of 1.50 m koh solution are needed to supply 0.125 mil of koh ?

The anwser cause i do not understand just plez

The figure shows the front side of a metal desk in the shape of a trapezoid. what is the area of this trapezoid? 10 ft²16 ft²32 ft²61 ft²