The variable z is proportional to x and inversely proportional to y. when x is 12 and y is 4, z has the value 57 what is the value if z when x=18 and y=10

The parabola opens: y=√x-4 (principal square root) up down right left

Titus works at a hotel. part of his job is to keep the complimentary pitcher of water at least half full and always with ice. when he starts his shift, the water level shows 4 gallons, or 128 cups of water. as the shift progresses, he records the level of the water every 10 minutes. after 2 hours, he uses a regression calculator to compute an equation for the decrease in water. his equation is w –0.414t + 129.549, where t is the number of minutes and w is the level of water. according to the equation, after about how many minutes would the water level be less than or equal to 64 cups?

Im so bad at fractions they are not my best math thing to work on