We need to buy mulch to cover an area 8 1/2 ft × 3ft × 6in. how many cubic feet of mulch are needed?

12.75 cubic feet

Step-by-step explanation:

Step 1:  Convert all measurements to feet since the answer is asking for feet.

The third measurement is in inches, so this is the one that needs to be converted.   Doing so give us the dimensions...

    8(1/2) x 3 x (1/2)           {6 inches is one-half of a foot, 12 inches to a foot}

Calculating volume of a three dimensional space is done by multiplying the three dimensions together.   If you have a calculator, convert the mixed fractions to decimals, then multiply the 3 numbers together...

   8.5 x 3 x 0.5  = 12.75

If you can't use a calculator, convert the mixed fractions to improper fractions and multipy...

   17/2 x 3 x 1/2    

      17/2 x 3/1  x 1/2       (3 is 3/1 written as a fraction)

       51/4          (multiply numerators together, multiply denominators

                          together)

        51/4 = 12.75      

the largest number of the four options is 1.8 x 10-2

you have it in scientific notation.

1.80 x 10-6   = 0.00000180

1.80 x 10-4   = 0.000180 (bigger, or "less small", than the former one)

so

1.8 x 10-2       = 0.0180. as you see. the "less small", or the biggest one of them all.

as you have negative exponent, it means you are dividing 1.8 by 100 (i.e. moving the dot towards left, two times).

if you had positive exponent for the scientific notation, power of tenths, you would be multiplying times 100 (moving the dot towards right) as below:

1.8 x (10)2 = 180

so. if you have negative exponent in scientific notation, move the dot toward left. if it is positive, toward right as many times the exponent tells you.