Write each expression in quadratic form, if possible x^4+12x^2-8
5x^6-2x^2+8
-15x^4+18x^2-4
9x^8-21x^4+12
16x^10+2x^5+6

Atown has a population of 17000 and grows at 2.5% every year. to the nearest year, how long will it be until the population will reach 19600?