3.5d + 5 represents the number of miles Erin ran last week when she ran 5 miles on
Sunday and 3.5 miles each day after Sunday.
The expression 2.5d + 3 represents the
number of miles Luis ran last week when
he ran 3 miles on Sunday and 2.5 miles each
day after Sunday.
a. Write an expression that can be used to
determine the total amount Erin and
Luis ran last week.
b. What is the total number of miles that
Erin and Luis ran through Thursday of
last week?

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.

(f+g)(x) = 3^x+10x+4x-2

      =3^x +14x-2

choice b