To add or subtract terms with exponents, both the base and the exponent must be the same. In this case they are so add the coefficients and retain the base and exponent:

-2a⁴ + 7a⁴
(-2 + 7)a⁴
5a⁴

A number in scientific notation has the format 0.000 x 10^exponent. To convert to scientific notation, move the decimal point to the right or the left until the number is a decimal between 1 and 10. The exponent of the 10 is the number of places you moved the decimal point and is positive if you moved the decimal point to the left and negative if you moved it to the right:

8,514,000 in scientific notation is 8.514 x 10⁶

If the tiger has consumed 70 pounds of food in 10 days that's \( \frac{70}{10} \) = 7 pounds of food per day. The tiger needs to consume 98 - 70 = 28 more pounds of food to reach 98 pounds total. At 7 pounds of food per day that's \( \frac{28}{7} \) = 4 more days.

In order to find how many additional workers are needed to staff the extra crews you first need to calculate how many workers are on a crew. There are 12 workers at the company now and that's enough to staff 4 crews so there are \( \frac{12}{4} \) = 3 workers on a crew. 6 crews are needed for the busy season which, at 3 workers per crew, means that the roofing company will need 6 x 3 = 18 total workers to staff the crews during the busy season. The company already employs 12 workers so they need to add 18 - 12 = 6 new staff for the busy season.

By buying two shirts, Ezra will save $38 x \( \frac{50}{100} \) = \( \frac{$38 x 50}{100} \) = \( \frac{$1900}{100} \) = $19.00 on the second shirt.