The sinusoidal function f(x)=42sin(9x−π10)+42 models the height, in centimeters, that a valve stem of the a tire is above ground x seconds after the tire begins to rotate. How long does it take the valve stem to complete one revolution?

Enter your answer, rounded to the nearest hundredth of a second, in the box.

a 4/6 = 9/12   not proportional

step-by-step explanation:

to find which are not proportional, we can use cross products

if it is true, they are proportional.   if it is not true, they are not proportional.

a 4/6 = 9/12

4* 12 = 6*9

48 = 54

not this is not proportional  

b 2/3 = 12/18  

2* 18 = 3 * 12

36 = 36

this is proportional

c 5/4 = 10/8  

5*8 = 4*10

40 = 40

this is proportional

d 7/5 = 35/25

7*25 = 5 * 35

175 = 175

is proportional

i don't see any

step-by-step explanation:

answer is because 4×10=40

and 98×4= is 392

40,392