Find the percentage of ratio to weight.
180/72 = 2.5
So 2.5 Earth Pounds = 1 Mars Pound
16*2.5 = 40 Pounds the rock weighs on earth.
Equation of a tangent line of a curve is:
y- y0 = f´ (x0) (x - x0 ). In this case: x0=1, y0=1
f´(x)=

(Derivation)
f´(x0)=

y - 1 = 1/2 ( x - 1 )
y - 1 = 1/2 x - 1/2
y = 1/2 x - 1/2 + 1
y =
A sequence of operations that will get you to the solution is ...
... d. multiply each side by-5, add 25 to each side
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That is not the only correct sequence of operations. However the other ones listed here are incorrect ways to get to x = -10.
You can do whatever multiplication and addition you like to each side of the equation, but if those operations are poorly chosen, they will make finding the solution more difficult.