Ineed with question 13
im struggling

You could create a equation such below:

y= 50x+20

Next, put 12 in both y=50x+20 and y=15x+80

Then, y=50x+20=50 · 12+ 20=600+20= 620

           y=15x+80=15 · 12+ 80=180+80= 260

Compare these two, it's clearly that the second one is cheaper

The camera in the second store is cheaper.

-2x + 7 = 7

subtract 7 from both sides.

-2x = 0

divide both sides by -2.

x = 0