Answer:
7
Step-by-step explanation:
Let p be the prize of a pen and m the prize of a mechanical pencils. If you buy six pens and one mechanical pencil, you spend 6p+m. We know that this equals 9, because you get 1$ change from a 10$ bill.
Similarly, if you buy four pens and two mechanical pencils, you spend 4p+2m, which is 8$, because now you get a $2 change. Put these equation together in a system:

Now, if you multiply the first equation by 2, the system becomes

Subtract the second equation from the first:

Plug this value into the first equation to get

Answer:
b = 55°
c = 35°
Step-by-step explanation:
b° = 180° - (85°+40°) = 180° - 125° = 55°
c° = 180° - (b°+90°) = 180° - (55°+90°) = 180° - 145° = 35°
3sqrt(2)
You can either use Pythagorean theorem or special triangle proportions to find the side that is parallel to z. Since in a 45-45-90 degree triangle, the hypotenuse is the leg times the square root of 2, and the hypotenuse is 3, we know that the leg is 3/sqrt(2) which is equal to 3 sqrt(2) / 2. Since z is twice this length, we know that z is equal to 2 x 3sqrt(2)/2 = 3sqrt(2)