There are 49 gallons of red paint.
I figured it out by doing the following:

If you subtract the gallons of pink paint (21) from the total number of gallons (70), then you get the number of gallons of red paint (49) because 49 + 21 = 70. I hope that helps :)
Answer:
#3.) The initial value of 16 gal at x = 5 minutes means that 16 gallons of water was present 5 minutes after the barrel started leaking.
#4.) Find how many minutes until the barrel is empty of water.
Let y = 0, to solve for time x.
0 = (-2/5)*x + 18
(2/5)*x = 18
x = (5/2)* 18 = 5*9 = 45 minutes
Up to and after 45 minutes, the barrel is empty of water.
Step-by-step explanation:
#2.)
minutes: 5, 10, 15, 20
water(gal): 16, 14, 12, 10
Find slope: slope m = (14 - 16)/(10 - 5) = -2/5
y - 10 = (-2/5)*(x - 20)
y - 10 = (-2/5)* x + 8
y = (-2/5)*x + 18
rate of change slope means that for every minute 2/5 gallons of water is lost
#3.) The initial value of 16 gal at x = 5 minutes means that 16 gallons of water was present 5 minutes after the barrel started leaking.
#4.) Find how many minutes until the barrel is empty of water.
Let y = 0, to solve for time x.
0 = (-2/5)*x + 18
(2/5)*x = 18
x = (5/2)* 18 = 5*9 = 45 minutes
Find the surface area of her notebook.
30 + 30 + 20 + 20 = 100
Now find the surface area of the square stickers.
2 + 2 + 2 + 2 = 8
So this is the surface area of one square, now multiply it by 8.
8 * 7 = 56
This is the surface area of all the stickers, now subtract it to the surface area of the notebook:
100 - 56 = 44
So 44 centimeters of the notebook cover will still be showing.