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

-1a³ - 7a³
(-1 - 7)a³
-8a³

Use PEMDAS (Parentheses, Exponents, Multipy/Divide, Add/Subtract):

4 + (5 + 4) ÷ 4 x 3 - 3²
P: 4 + (9) ÷ 4 x 3 - 3²
E: 4 + 9 ÷ 4 x 3 - 9
MD: 4 + \( \frac{9}{4} \) x 3 - 9
MD: 4 + \( \frac{27}{4} \) - 9
AS: \( \frac{16}{4} \) + \( \frac{27}{4} \) - 9
AS: \( \frac{43}{4} \) - 9
AS: \( \frac{43 - 36}{4} \)
\( \frac{7}{4} \)
1\(\frac{3}{4}\)

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:

0.0001673 in scientific notation is 1.673 x 10^-4

The first few multiples of 4 are [4, 8, 12, 16, 20, 24, 28, 32, 36, 40] and the first few multiples of 12 are [12, 24, 36, 48, 60, 72, 84, 96]. The first few multiples they share are [12, 24, 36, 48, 60] making 12 the smallest multiple 4 and 12 have in common.

If the tiger has consumed 78 pounds of food in 6 days that's \( \frac{78}{6} \) = 13 pounds of food per day. The tiger needs to consume 156 - 78 = 78 more pounds of food to reach 156 pounds total. At 13 pounds of food per day that's \( \frac{78}{13} \) = 6 more days.