Answer:
( -1 , 26)
Step-by-step explanation:
So since you need to find the other endpoint, you would follow these steps:
1.) 
2.) 8 = 9 + x ( you just multiplied the 2 to the 4 to get 8)
3.) -1 = x (just solve it like a regular equation, so just subtract 9 on both sides to get rid of it and that leaves you with -1 = x)
You took the x values of both points and put them in the equation.
And its the same for y
1.) 
2.) 16 = -10 + y
3.) 26 = y (you added the 10 on both sides because the 10 was negative and that took the 10 out and so it left you with 26 = y)
The equation for this is a^2+b^2=c^2 so your equation would be 7^2+20^2=X
So you square the 7 and the 20 then take the square root of X and you get
X=21.19
:)
X is 66 degrees, you just subtract 24 to 90 and it gives you 66.