Can some one please help me solve this ?

You're in high school.  You learned a long time ago that the distance between
any two points is . . .

square root of [ (difference in their x-values)²  +  (difference in their y-values)² ].

Your two points are  (-9, 6)  and  (-3, 9).

The difference in their x-values is  6 .
The difference in their y-values is  3 .

The distance between the points is . . .

 square root of [ (6)²  +  (3)² ]  =  √(36 + 9)  =  √45

So this can be set up like a triangle and use that pythagorian theorem
a^2+b^2=c^2
so to find a you subsitute (x₁-x₂) and for b subsitute (y₁-y₂)

we want to find c
so
(-9-(-3))^2+(6-9)^2=c^2
(-9+3)^2+(6-9)^2=c^2
(-6)^2+(-3)^2=c^2
36+9=c^2
45=c^2
square root both sides
√45=c=distance
√45=3√5 in other words 3 times √5

answer is 3√5