First, subtract the x values - in any order - and square the result
(-5-3)2 = (-8)2 = 64
Then, subtract the y values - in any order - and square the result
(-3-9)2 = (-12)2 = 144
Add the two results
64 + 144 = 208
Take the square root of this
√208 =√( 4*52) = √(4*4*13) = √(16*13) = 4√13 ....or......about 14.42, if you prefer...