Cos(sin⁻¹(³/₅))
cos(36.87)
0.79
1/4 * 1/3 * 1/2 * 1/1 = 1/24 chance that all 4 letters are placed in the correct envelopes.
With the first envelope, there are 4 choices of letters, so the probability of picking the correct letter is 1/4.
With the second envelope, there are 3 remaining letters, so the probability of picking the correct letter is 1/3.
The same logic follows the the third and final letter.
And you know how much you are going through the relationship with your friends you are so happy and
#8) Subtract 350 from each side then divide each side by 25 to get (c-350)/25 = h.
Plug in 950 for c to get (950-350)/25 = h.
600/25 = h = 24 hours.
#9 is the same as number 8 just with one more variable. Subtract 2.25h from both sides and divide both sides by 1.75. Then plug in 18.25 for t and 5 for h. Then solve for d.
We need to get the variable on one side (usually the left side) and all other constants (like numbers and certain symbols like

) on the opposite side of the variable (usually the right side).
4(2s - 1) = 7s + 12 // Our starting equation
8s - 4 = 7s + 12 // Distribute the 4 across the 2s and the -1
s - 4 = 12 // Subtract both sides by 7s
s = 16 // Add both sides by 4
The variable s is equal to 16.