Find an integer value of b that makes x^2+bx-81

If 10 men take 18 days to mow 60 acres of grass, how long will 15 men take to mow 80 acres?

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

What is the area of the original rectangle? 8 cm² 20 cm² 25 cm² 40 cm²