I need to understand the solution.

D) $60.40

Step-by-step explanation:

The price is marked up by 20%.  If we say the original price is P, then the new price is P + 0.2P = 1.2P.  So the new price must be a multiple of 1.2.

If we divide each option by 1.2:

A) $1.20 / 1.2 = $1.00

B) $70.80 / 1.2 = $59.00

C) $6.00 / 1.2 = $5.00

D) $60.40 / 1.2 = $50.333...

E) $150.60 / 1.2 = $125.50

Option D can't be the new price.  There's no such thing as a one-third penny.

c.

step-by-step explanation:

she should of added 9^2 and 12^2. that is because it is a^2+b^2=c^2. c^2 is the hypotenuse and should always be bigger than the other two numbers. which is why she should of added 9 squared and 12 squared together instead of 15 squared.