we have the system of equations
y=3x+4 ----> equation 1
y=ax+b ----> equation 2
Remember that
The only condition for the system, to have only one solution is that the slopes of both lines are different
so
The values for a are all real numbers except for a=3
The values for b are all real numbers
Therefore
A solution could be
a=2 and b=4
The solution is (0,4)