Best is to draw a sketch of the three points.
Next step is to find the distances BC, CD, DB.
The perimeter is the sum of the three distances.
The distances are found using the distance formula:
D=sqrt((y2-y1)^2+(x2-x1)^2)
order of (x1,y1), (x2,y2) is not important.
BC=sqrt((3- -3)^2+(5-3)^2)=sqrt(6^2+2^2)=sqrt(40)=5.324
CD=sqrt((-1-3)^2+(0-5)^2)=sqrt(4^2+5^2)=sqrt(41)=6.403
DB=sqrt((-3- -1)^2+(3-0)^2)=sqrt(2^2+3^2)=sqrt(13)=3.606
So perimeter = BC+CD+DB=16.333 (approximately)
