Simple interest =`(P xx R xx T)/100`
where P is the principal amount , R is the rate and T is time.
1. P=4500,R=4,T=0.5
applying in formula, simple interest=Rs.90
2.1. P=12000,R=18,T=`1/3`
applying in formula, simple interest=Rs.720
3.1. P=1000,R=10,T=0.2
applying in formula, simple interest=Rs.20