Solve for t. d=−16t^2 +4t

C option is correct.

t = 8 +- √ 1− 4 d

Step-by-step explanation:

d=−16t^2 +4t

t= (1+ √ 1− 4 d) /  8

 t = (1 − √ 1 − 4 d  ) / 8

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