At first you have to write the variables out which are

now you have to combine like terms


now you add these two variables and end up with answer of
Answer:
They have a shared economy.
They allow easy migration
Using the principles of cross-cutting relationships, you can determine the relative age of rocks found in the ground. The idea behind it is that the geologic feature which cuts another is the younger of the two features, and it had been around for 400 years. It's not very precise but it is good for determining relative age.
A measure of the amount of light given off by a star is its absolute luminosity or magnitude. Absolute magnitude<span> is the measure of </span>intrinsic brightness<span> of a celestial object. It is the hypothetical </span>apparent magnitude<span> of an object at a standard </span>distance<span> of exactly 10 </span>parsecs<span> (32.6 </span>light years<span>) from the </span>observer<span>, assuming no </span>astronomical extinction<span> of starlight. </span>