Question 253065
.08*12000*6=5760 money invested at 8% for six years 
6*3300=19800
12000+5760=17760
19800 is larger than 17760
if they purchase it it will cost 12000+5760
cost plus interest not earned
if they rent it will cost 19980-interest earned


696 interest 1 year 8700 on 12000-3300
432 interest 2 year 5400 on 8700-3300
168          3 year 2100 on 5400-3300
0            4 year 00000 on 2100-3300
696+432+168 =1296 interest for three years
19980-1296=18684 cost for leasing+interest for 3 years on the remainder of 12000

cost for purchasing=12000+5760(interest lost)=17760
so it still comes out better to buy it
actual costs
18684 versus 12000 
Since the leasing is so much more than purchase the interest for six years really don't come into play here.
It would be significant if the leasing were cheaper.