Answer:
42
Explanation:
In short, the sum of the opposite areas are equal.
x + 30 = 24 + 48
x = 42
To prove this, draw a line from each corner to the "center" where the four lines meet. Along each side of the square are two triangles. These triangles have the same base and the same height, and therefore have the same area.
If we say the triangles at the bottom have area a, the triangles on the left have area b, the triangles on top have area c, and the triangles on the right have area d, then we can write 4 equations:
a + b = x
b + c = 24
c + d = 30
a + d = 48
Adding the first and third equations:
a + b + c + d = x + 30
Adding the second and fourth equations:
a + b + c + d = 24 + 48
Therefore:
x + 30 = 24 + 48
x = 42