Answer:
b= 4a-c
Step-by-step explanation:
There isnt an actual number you can solve for here so just say what b equals to.
4a-b=c
Move b
4a=b+c
Move C
4a-c=b
You estimate the product by rounding to the nearest 10:
9 becomes 10 and 54 becomes 50
9 x 50 = 450
That would be B, C and E.
A and D could be a rhombus.