Which system of equations models this problem?
the variable x represents the number of angelfish carlos bought and the variable y represents the number of parrotfish he bought.
carlos bought 405 tropical fish for a museum display. he bought 8 times as many parrotfish as angelfish. how many of each type of fish did he buy?
a
x−y=405
y=8x
b
x+y=405
y=8x
c
x+y=8
y=405x
d
x+4y=8
y=405x

Carmen and matt are conducting different chemistry experiments in school. in both experiments, each student starts with an initial amount of water in a flask. they combine two chemicals which react to produce more water. carmen's experiment starts with 30 milliliters of water in a flask, and the water increases in volume by 8.5 milliliters per second. matt's experiment starts with 10 milliliters of water and increases in volume by 28% each second.