Both charms are "similar".
And notice one diameter is 1, the other is 4, the diameters are on a ratio of 1:4 then, and so both figures are on a ratio of 1:4.
so, if another unit, like the circumference is at 3.14 on the small one, then the large one will have a circumference 4 times that much, because the circumferences are also on a 1:4 ratio.
The only number equal to zero is zero.
Answer: a = 0
