If f(x) is parallel to the line y=3/4x+b ,it would have to have the same slope.
In this equation:
y=mx+b
m= is the slope of the line.
A line parallel to the line y=3/4x +2/5 must have the same slope; that it is to say, the slope would be m=3/4
Examples:
y=3/4 x+ 50000
y=3/4 x -51/36
y=3/4 x -√2
These functions could be parallels to the line y=3/4 x +2/5