A principal of $800 was invested, part at 9% and the rest at 12% per annum. After one year, the the total interest earned was $79.95. How much was invested at each
rate

if you are saying purchasing 3 social media ads and one newspaper ad counts as one purchase then there are:

6 purchases

if you are asking how many of each then:

18 social media ads

6 newspaper ads

i got 10.28 but that rounds up to 10.3