To simplify 3( -x + y ), we can use the distributive property.
The distributive property states that
a( b + c ) = ab + ac
Basically the a is distributed to the terms inside the parenthesis, the a is multiplied by b and added to a multiplied by c
For this problem 3 ( -x + y), the 3 is like a. It is outside the parenthesis and needs to be distributed.
So multiplied is 3 * -x + 3 *y
= -3x + 3y