I’m having a hard time with this

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

45 was divided by a power of ten to get 4.5. what power of ten was it divided by? people 4.5

2x minus y equals 6, x plus y equals negative 3