The answer is 2.5 because the point is on -1.5, so -1.5+4=2.5
Time= 6 1/4= 25/4
Principal- Rs x
Rate=?
Rate=100 * Simple Interest
Rate= 100*3x*4 divided by x*8*25
Rate=6%
Consider,

. Let's say

then the problem reduces to

. (Do you understand this step?)
So then replacing a again with our definition we get,

.
One dozen= 12
$1.80/12= $0.15 each
Final answer: $0.15