What is the domain of the function shown in the mapping?

a.) {x | x = –5, –3, 1, 2, 6}
b.) {y | y = –9, –6, 0, 2, 4}
c.) {x | x = –9, –6, –5, –3, 0, 1, 2, 4, 6}
d.) {y | y = –9, –6, –5, –3, 0, 1, 2, 4, 6}

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?