Can anyone tell me how to solve number 13 ?

Solve 13 + w/7= -18 (w/7 is a fraction)

The sum of two numbers is 0. twice the smaller number subtracted from 3 times the larger number is 10. let x represent the larger number and y represent the smaller number. what is the equation

Suppose that prices of a gallon of milk at various stores in one town have a mean of $3.71 with a standard deviation of $0.10. using chebyshev's theorem, what is the minimum percentage of stores that sell a gallon of milk for between $3.41 and $4.01? round your answer to one decimal place.