<u>Answer-</u>
<em>At 15.91° the ball was thrown.</em>
<u>Solution-</u>
<em>In the question it is given that the ball was released and caught from the same height.</em>
We know that,

Where,
R = Range of the projectile = 7.75 m,
u = Initial speed = 12 m/s
θ = Angle at which it was released
g = Acceleration due to gravity = 9.8 m/s²
Putting all the values,





The first one is k=2 and the second answer is 0 so basically all you doing is adding the equations
Box 1 : 3 pencils + 7 pens = total of 10
probability of picking a pen is 7/10
box 2 : 3 pencils + 3 crayons = total of 6
probability of picking a crayon is 3/6 which reduces to 1/2
probability of picking both is (7/10 * 1/2) = 7/20 <==