To isolate the variable, you need to divide both sides of the equation by three, using the division property of equality. 126/3=42 , and 3x/3=x , this gives you 42=x, or x=42, meaning the answer is D.
this is because the heart is more muscle than anything! Muscle cells have loads of mitochondria and the mitochondria themselves are even more efficient than your average mitochondria.
