What is the difference between an expression and an equation?

Imogene invested $8,000 in a bank account that pays 8 percent simple interest at the end of each year. her friend invested the same amount in stocks where the growth of the investment is represented as 2,000 times the square root of 2 less than the time lapsed in years. if y1 and y2 represent the amount earned in dollars and t is the time lapsed in years, which system of equations correctly represents the situation?

The radius of the earth is two times the radius of the moon. what fraction of the volume of the earth is the volume of the moon?

What is 1/3x5 on anuber line what does it look like on a number line