Answer:
15
Step-by-step explanation:
The total number of teachers in the school is 100.
The number who teach Science is 60
The who teach humanities is 25.
The number that teach both humanities and Science is 15.
We want to find the number who teach Science but not Humanities.
We obtain this by subtracting the number of teachers who teach both subjects from the number that teach Science.

Therefore 25 teaches science but not Humanities
So.. let's say ∡AGB and ∡BGC are say "a" units wide, and ∡CGD and ∡DGE are "b" units wide
notice the picture below
all angles added up together, will make up just a flat line, or 180°
now, notice in the picture, the ∡BGD is really just " a + b " wide, notice the green angle in the picture of ∡BGD, well, we know what a + b is
A 80 square meter I’m not quite sure
Multiplying fractions is simple. You just multiply across so 7/3 x 2/3 is 14/9 and that is the simplest form.
Multply both equations by 2 leaving
x + 2y = 8
x - 2y = -2
Add the equations giving
2x = 6
x = 3
Substitute 3 in the top equation
3 + 2y = 8
2y = -5
y = -2.5