Proportional reasoning is the ability to compare two things using information given, in math, it is most frequently defined as comparing quantities. For something to be proportional, there has to a constant ration of another quantity.
There are 1000 meters in 1 kilometer so you can set up a proportion to find the number of meters. 1000m / 1km = x / 40075 km cross multiply and you get the answer of 40,075,000 meters. To change to scientific notation, move the decimal point next to the 4 (becuase 4.0075 is less than 10) and you get the answer of 4.0075 x 10^7 meters.
√z = 13 - 8
√z = 5
z = 5²
z = 25
In this case the z can be any number, however z cannot be less than 0 and that is the restriction. (for example; √-1 = irrational number, cannot be solved.)
