If you are looking for x then it is X = 18
Answer:
15
Step-by-step explanation:
x - y = 10, then x = 10 + y
x + y = 20
substitute for x:
10 + y + y = 20
2y = 10
y = 5
x = 10 + 5 = 15
Answer: 410 square km
Step-by-step explanation:
The area of each of the triangles with their base on the 10 km side is
, so their combined area is
.
The area of each of the triangles with their base on the 12 km side is
, so their combined area is
.
The area of the bottom rectangular face is
.
So, the total surface area is 
Yes, not a equallateral but an issoceles