First thing you want to do is put v by itself
Add 90 to both sides
2v^2 = 90
Divide by 2 on both sides
v^2 = 45
And then take the sqrt(45)
v = sqrt(45)
We can reduce this by finding the perfect square which is 9
v = sqrt(9) * sqrt(5)
So,
v = 3 * sqrt(5)