There are 15 numbers such that average of first 12 numbers is 30 while the average of last five numbers is 50. Find the 12th number, if the ratio between 11th and 12th number is 6:5, respectively.

I. x² – 10x + 21 = 0

II. y² + 11y + 28 = 0

I. 2y² - 35y + 132 = 0

II. 2x² - 31x + 110 = 0

I. 24x² - 58x + 23 = 0

II. 20y² + 24y – 65 = 0

I. √(74x-250 )– x=15

II. √(3y²-37y+18)+ 2y=18

I. 2y²- 37y + 143 = 0

II. 2x²+ 15x – 143 = 0

I. 2x² + 12x + 18 = 0

II. 3y² + 13y + 12 = 0

I. x² + 16x + 63 = 0

II. y² + 2y - 15 = 0

A and B are the roots of equation x² - 13x + k = 0. If A - B = 5, what is the value of k?

I. (x^13/5 ÷7) = 5488 ÷ x^7/5

I. 117x² + 250x + 117 = 0

II. 54y² -123y + 65 = 0