Ratio 390mm to 13 cm as fraction in the lowest term

Marcus's card monthly Comcast bill is $54 if he watches no On Demand movies. However, for every On demand movies that Markus watches in a month, he pays $8. write an equation answer

Twenty less than three times a number is the same as six less than the number

How do I find x? Because I can not find the answer

Until the truck runs out of gas, the amount of gasoline it's fuel tank varies inversely with the number of miles traveled.

Original price - $82. Percent of discount-? Sale price - $65.60

Leah is placing books on a one meter long shelf. If each book is 2 cm wide, how many books will fit on the shelf?

Rex mixed x liters of fruit syrup with y liters of water to make a fruit punch. Three times the number of liters of water he mixed was 6 more than twice the number of liters of syrup he mixed.

There are 4 red paint cans, 2 green paint cans, and 1 yellow paint can. What is the probability of choosing a yellow paint can then a red paint can without replacement?

on a map, two cities measure 6.2 cm apart. If the scale of the map is 5 cm per 10 miles, then how many miles apart are the cities

8x-3x=20 show work to receive credit.