Put f(x) = 2 -e^x;

Then f'(x) = -e^x;

At (2.485,0) x = 2.485 and f'(x) = -[e^(2.485)] = -(12.00112025). Some may prefer to

round this of to -12.

y= 12 - e^x

y'= -e^x

y'(2.485)= -e^(2.485)≈ -12