y-axis = altitude in feet
x-axis = minutes
slope = y/x = feet/minute
According to above data, we know that 1800 feet is y-intercept and slope is -300 feet per minute (why slope is negative? because its approaching ground at a constant speed)
a. slope = -300
y-intercept = 1800
b. y = -300 x + 1800
c. Here we are given x = 2 minutes
y = -300(2) + 1800
y = -600 + 1800
y = 1200
The balloon will be 1200 feet high above the ground in 2 minutes.
d. Here we are given 300 feet which is y, and find x minutes.
y = -300 x + 1800
300 = -300x + 1800
300 - 1800 = - 300x
-1500 = -300x
1500 = 300 x
x = 1500 / 300
x = 5
The balloon will reach 300 feet above the ground in 5 minutes.
e. It asking when the balloon will reach the ground, if the balloon reaches the ground than the height will be 0, therefore x-intercept (y=0).
y = -300 x + 1800
0 = -300 x + 1800
-1800 = -300x
1800 / 300 = x
x = 6
The balloon will reach the ground in 6 minutes.
//Hope this helps