5 more than the product of a number and 4 is equal to 3 use variable y for unknown number

Which triangle congruence postulate or theorem justifies my claim that the steps i made using construction paper and scissors produce an isosceles triangle? was it sss, sas, asa, aas, or hl?

Solve the given system of equations. 2y= -x+9 , 3x-6= -15

Me, the vertices of quadrilateral coat are c(2,0), o(7,0), a(7,2) and t(2,2). prove that coat is a rectangle.