Answer:
rearrange them properly to get
x-y=7
-3x+y=12
( by elimination method)
x-y = 7
-3x+y=
(x+ –3x) + (–y+y) = (7+12)
-2x+0= 19
x= -9.5
from eqn(i)
x-y=7
-9.5 - y=7
-y=16.5
y= -16.5
30 x 30 = 900
This is the surface area of one side
900 x 6
Multiply by 6 to get the surface area of all 6 sides of the cube
900 x 6 = 5400
40%less
You take 36/60
That equals 60%
This means that 36 is 60% of 60
So in 24 is 40% of 60 or 36 is 40% less than 60
For this case we have the following equation:

Where,
w: The weight of a spring in pounds
E: the energy stored by the spring in joules.
Substituting values we have:

Making the corresponding calculation:
Answer:
the approximate weight of the spring in pounds is: