To simplify #-(5y - 6) + 4(3 +5y)# you would first use the Distributive Property then Combine Like Terms. The Distributive Property is where you take the Numbers outside the Parenthesis and Multiply it with each number in the parenthesis.
Example of the Distributive Property:
#2(3-6)#
#6-12#
#-6#
This only works with addition and subtraction inside the parenthesis, after multiplying keep the sign separating the two numbers and then solve as normal.
Solving your Equation:
#-(5y - 6) + 4(3 +5y)# is Original problem
#-5y + 6 + 12 + 20y# is After using the Distributive property
#15y + 18# is After Combining Like Terms. This is also your final answer.