Can someone good at math give me a hand i really need some w

What is the solution of sqrt x+2-15=-3

The transitive property of equality states that: o if a = b, then bra o if a = b, then ac = bc o if a = b and b= c, then a = if a = b and c= c, then a + b = b + c

Which property was used to simplify the expression? 3c+9 +4c=3c+4c+9