"In each formula, C represents the cost x years after 1980 of what cost $10,000 in 1975.

C=865x+15,316

C=-2x^2+900x+15,397

Use model 1 to determine the cost in 2000."

My work:

C=865(25)+ 15,316

C= 36,941

"Use model 2 to determine the cost in 2000."

My work:

C=-2x^2+900(25)+15,397

C= 36,647

Both were wrong. I subtracted 1975 from 2000 to come up with x.