Answer:
the horizontal are called x-axis, while the vertical are called y-axis
Let the full marks be represented by = x
As given, 80% of x is 75
So,

x= 
x=93.75
Hence, full marks is 93.75
We can check also-
=75
The marching l meaning of the X intercept is when the school receives $0
1 - 1/2c = 6
1 -1 - 1/2c = 6 -1 (subtract 1 on both sides)
-1/2c = 5 (next do the inverse operation)
c = 5 ÷ 1/2
c = -10
to check your answer substitute the value of c in the equation;
1- 1/2c = 6
1- 1/2(-10) = 6
1 + 5 = 6
6 =6
Mass error is due to temperature which is a random error. I believe.