What is (5x - 3x^2)-(5x - 2)( 10x + 7x^2) in standard form

Describe all the numbers that when rounded to the nearest thousand are 645,000

Aswim teacher sells lesson packages. the best deal has the highest ratio of lessons to total cost.swim lesson packagesnumber of lessons total cost$10$4010 1 $8015$80which package is the best deal? l lesson for $105 lessons for $4010 lessons for $8015 lessons for $80mark this and returnsave and exit

How do you use the elimination method for this question? explain, because i really want to understand!