It should be a.), all plant cells have a cell wall made of cellulose, which acts as exoskeleton and makes them so stable. However on a bigger level this plant cells can also form cellulose fibers, so that c.) is not completely false :)
I don’t know The answer but I tried
12x-4y=16
Isolate Y:
Subtract 12x from both sides
-4y=-12x+16
Divide by -4
y=3x-4
Therefore the slope is 3
To find what she saved you need to subtract
500-325= 175
then take 175 divided by the original price (500) to get a percentage so
175÷500=0.35
0.35= 35%
so your answer is she saved 35%