5c-6c+8c-9c can some one simplify this

-2

Step-by-step explanation:

Just add up the coefficients, forming a single coefficient:

(5 - 6 + 8 - 9)c = -2

For part one, round the number of seconds in a year, to an easy number, depending on how many significant figure then divide that by 3600, the number of seconds in an hour to get the number of hours in a year. for part 2 do the same but use the exact number instead of the rounded, scientific notation is expressed by using a number between 1 and 10 multiplied by a power of 10 which is how many digits to the left (positive exponent) or right (negative exponent) you must move to get a number from 1 to 10
for part three just explain what is the same or different about your 2 answers.