Question 44712
The first step should be to make the right hand side equal to zero:
{{{b^2 - 3b = 5}}}
{{{b^2-3b-5=0}}}
Now try completing the square:
{{{(b-(3/2))^2-5-(3/2)^2=0}}}
{{{(b-(3/2))^2-5-(3/2)^2=0}}}
{{{(b-(3/2))^2-5-(9/4)=0}}}
{{{(b-(3/2))^2-20/4-9/4=0}}}
{{{(b-(3/2))^2-29/4=0}}}
Now rearrange to find b:
{{{(b-3/2)^2=29/4}}}

{{{b=3/2+-sqrt(29/4)}}}
{{{b=3/2+-sqrt(29)/2}}}
{{{b=(3+-sqrt(29))/2}}}

I hope this helps.
P.S. I am trying to start up my own homework help website. I would be extremely grateful if you would e-mail me some feedback on the help you received to adam.chapman@student.manchester.ac.uk
Adam