Which graph represents a linear function?

The graph represents the gallons of water in a water tank with respect to the number of hours since it was completely filled

Me its important ! marge runs an ice cream parlor. her speciality is triple chocolate sundaes.she can prepare 1 sundae every 2 minutes, and she earns $1.20 for each sundae she makes . if she just makes sundaes for a single shift of at most 4 hours and at least 2 hours , which function relates her earnings to the number of minutes she works?

What is the y-intercept of the line with the equation 3x + 4y = 12?