Step-by-step explanation:
It's the <em>DISTRIBUTIVE PROPERTY</em>:
m(a + b) = ma + mb
Other properties:
Commutative Property:
<em>of addition: a + b = b + a</em>
<em>of multiplication: a · b = b · a</em>
Associative Property:
<em>of addition: (a + b) + c = a + (b + c)</em>
<em>of multiplication: (a · b) · c = a · (b · c)</em>