$40/12 = unit rate simplify = 10/3
$10/3 per book
18 * 10/3 = $60 for 18 copies
3: multiply the change per minute by how many minutes: 3.1x15=46.5. 5: Is your opinion, I can't tell you how to feel. But a negative times a negative is a positive, so if there is an even number of negatives no matter how many positives there are it will be positive, if there is an odd number of negatives it will be negative. :) Hope this helps!
Let x = cost of desktop computer; then x - 250 = cost of laptop computer
converting % to decimals, 9% = 0.09 and 6% = 0.06
Then, 0.09x + (x - 250)0.06 = $300
0.09x + 0.06x - 15 = $300
0.15x = $315
x = $2100
then x - 250 = $1850
Proof: $2100•0.09 + 1850•0.06 = $189 + $111 = $300
