On Tuesday and Friday there would be enough teachers. To find this answer divide the number of kids by 12, and see if the answer is below the number of students.
Tuesday - 179/12=14.9 - there are 15 teachers - enough
Wednesday - 162/12=13.5 - there are 13 teachers - not enough
Thursday - 170/12=14.1 - there are 14 teachers - not enough
Friday - 143/12=11.8 - there are 12 teachers - enough
Hope I explained that good enough :)