Need help ASAP please and thank you.

In right ∆abc shown below, the midpoint of hypotenuse ac is located at d and segment bd is drawn.if ab = 12 and bc = 16, then explain why bd = 10. hint: consider what you know about the diagonals of a rectangle.

What is the value of x when x + 7 = 21?

What is the value of n in the equation -1/2(2n+4)+6=-9+4(2n+1)