What is the true solution to the equation below ?

2 In e^ln 2x– In en^ 10x = In 30

x=30
x=75
x=150
x=300

If y varies directly as x2 and y=6 when x=6, find the constant of variation.

Solve this riddle: i am an odd number. i an less than 100. the some of my digit is 12. i am a multiple of 15. what number am i?

How many quarts of a 50% solution of acid must be added to 20 quarts of a 20% solution of acid in order to get a 40% solution of acid?