Length of st is 16
Since p is the midpoint of st, that makes sp half of st.
So
sp = x+4 Given
st = 4x Given
st = 2(sp) length of st is twice length of sp
st = 2(x+4)
Set the two different ways of describing st equal to each other.
4x = 2(x + 4)
Distribute the 2
4x = 2x + 8
Subtract 2x from both sides
2x = 8
Divide both sides by 2
x = 4
Now substitute the value 4 for x in the length of st
st = 4x
st = 4*4
st = 16.
