4:
a) if a cloud is a mid-level cloud, then it is between 6,500 and 20,000 feet.
b) if a cloud isn't a mid level cloud, then it is not between 6,500 and 20,000 feet. [I don't know if this statement is true]
8:
P=2l+2w
solve for w means to make the equation like w=... (get w on one side by itself).
First, subtract 2l from both sides
P-2l=2w
Now, divide both sides by 2
= 
Done
9:
*The question is a bit wrong here; it should have said In the corner of the angle ABC there is a little square symbol - that means it is a 90 degree angle.
The angle ABC is broken up into angles ABD and DBC, so ABD and DBC add up to 90 degrees.
So, we can make the equation (2x + 10) + (x + 14) = 90
Then solve
Since it is all addition, the parentheses are unnecessary
2x + 10 + x + 14 = 90
Add all x terms together, and the numbers together
3x + 24 = 90
Subtract 24 from both sides
3x = 66
Divide both sides by 3
x = 22
Now, plug in this x value into the formulas for the two angles
ABD = 2(22) + 10 = 44+10 = 54 degrees
DBC = 22 + 14 = 36 degrees
a) if a cloud is a mid-level cloud, then it is between 6,500 and 20,000 feet.
b) if a cloud isn't a mid level cloud, then it is not between 6,500 and 20,000 feet. [I don't know if this statement is true]
8:
P=2l+2w
solve for w means to make the equation like w=... (get w on one side by itself).
First, subtract 2l from both sides
P-2l=2w
Now, divide both sides by 2
Done
9:
*The question is a bit wrong here; it should have said In the corner of the angle ABC there is a little square symbol - that means it is a 90 degree angle.
The angle ABC is broken up into angles ABD and DBC, so ABD and DBC add up to 90 degrees.
So, we can make the equation (2x + 10) + (x + 14) = 90
Then solve
Since it is all addition, the parentheses are unnecessary
2x + 10 + x + 14 = 90
Add all x terms together, and the numbers together
3x + 24 = 90
Subtract 24 from both sides
3x = 66
Divide both sides by 3
x = 22
Now, plug in this x value into the formulas for the two angles
ABD = 2(22) + 10 = 44+10 = 54 degrees
DBC = 22 + 14 = 36 degrees