Which if the following is not a characteristic of both observational studies and experiments
a . the subjects are observed, and their behavior is recorded
b. results are not used to prove cause and effect
c data are collected about population
d. the researcher exercises direct control over at least one variable

12 servings. 4 times 3= 12

your answer is 23/2 - 13.5

step-by-step explanation:

7/2 evaluates to

multiply x and 4.5

multiply x and 1

the x just gets copied along.

the answer is x

x

4.5*x evaluates to 4.5x

multiply 3 and 4.5x

multiply 1 and x

the x just gets copied along.

x

4.5*x*3 evaluates to 13.5x

7/2-4.5*x*3 evaluates to

  + 8 =

the answer is

7/2-4.5*x*3+8 evaluates to