Book cost 12.87 for 9kg how much does 1 kg cost to the nearest cent

The last time i bought this product , it cost $20.00 but it looks like it cost 29. 60 today? what is the increase

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

When 142 is added to a number the result is 64 more then 3 times the number. option 35 37 39 41