Determine a function with the given properties. Help!

So i have the following properties of a function given, and need to determine the (a) function:

 

• f is continuous
• f(x) = x   for x<0
• f(1) = 3/4
• x=3 is the global maximum of f

I have a vague picture of f, but I have no idea how I get the equation, help me please!