Idk im just tryna complete a challenge lol
Answer:

Step-by-step explanation:
3 envelopes having 2 red card
2 envelopes having 1 red card and 1 black card
1 envelope having 2 black cards
We are given that . An envelope is selected at random and a card is withdrawn and found to be red.
So, No. of ways of envelope having red card = 3+2 = 5
No. of required ways of envelope having 1 red card and 1 black card = 2
So, probability of getting an envelope having 1 red card and 1 black card = 
Hence The chance the other card is black is 
When the firecracker hits the ground, H(t) = 0.0 = -16t^2 + 90t + 160 Using the quadratic formula,t = (-90 +- sqrt(90^2 - 4(-16)(160))) / 2(-16)t = -1.42 ort = 7.04
The negative time is extraneous. Therefore,t = 7.04 s.
Seven Seconds is your answer!