Easy Problem made frustrating

d^2y/dx^2 = 0.5dy/dx where y=0 and dy/dx=3 when x=0

We have to find what y is when x=5

My solution keeps turning out to be y=6e^5/2 - 6

However the back of my textbook says y=6e^5/2 - 6e^2

Here is how i did it

let v = dy/dx

therefore d^2y/dx^2 = vdv/dy

vdv/dy = 0.5v

dv=0.5dy ... intergrate both sides

v=0.5y + C

3=0.5(0) + C

C=3

v=0.5y + 3

dy/dx=0.5y + 3

2dy/y+6 = dx

2loge(y+6) = x + B

B = 2loge(6)

2loge(y+6/6)=x

y+6/6=e^x/2

y=6e^5/2 - 6

Where have I gone wrong and what is the correct way to do it if i am wrong???