What property is being illustrated: 19 + 0 = 19

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?

The lines shown below are parallel. if the green line has a slope of -1, what is the slope of the red line?

Based on the graph, what is the initial value of the linear relationship? a coordinate plane is shown. a line passes through the y-axis at -2 and the x-axis at 3.