I'm guessing that this is a problem to find the weight of a 90kg mass on a planet where the acceleration of gravity is 4 m/s^2. (Much less gravity than Earth, a little more than Mars.)
Just do the multiplication, and you get
360 Newtons.
Answer:

Explanation:
From the question we are told that:
Mass 
Angle 
Coefficient of static friction
Generally, the equation for Newtons second Law is mathematically given by
For


for


Where



Therefore



Every practical source of energy that you can imagine, as well as a few impractical ones, are used somewhere in the USA.
From whale oil in Alaska, to nuclear energy, to coal, petroleum, natural gas, solar energy, wind energy, and biomass.
Oh ! Geothermal energy and tidal energy aren't too popular, but I'll bet if you looked, you'd find these used too, SOMEwhere in the 50 states.
General relativity is the theory of space and time. This was theory was found by Albert Einstein