What does 16/6 equal to as a whole number

For the rule of 78, for a 12-month period, the last term in the sequence is 12 and the series sums to 78. for an 10 month period, the last term is and the series sum is . for a 15 month period, the last term is and the series sum is . for a 20 month period, the last term is and the series sum is

If f(x)=3x+1 and f^-1=x-1/3, then f^-1(7)=

Atriangle has a side lengths of 18cm, 80 cm and 81cm. classify it as acute obtuse or right?