Write both fractions in terms of a common denominator. In this case, it's the least common multiple of 6 and 12, which is 12 = 2•6. So multiply the first fraction by 2/2, then simplify:
[tex]\dfrac46 - \dfrac3{12} = \left(\dfrac22\times\dfrac46\right) - \dfrac3{12} = \dfrac{2\times4}{2\times6}-\dfrac3{12} = \dfrac8{12}-\dfrac3{12} = \dfrac{8-3}{12} = \boxed{\dfrac5{12}}[/tex]
