Solve the following system of equations:
x − 2y = 5
2x − 4y = 10

part a.

angle addition postulate:

if a point lies on the interior of an angle, that angle is the sum of two smaller angles with legs that go through the given point.

from the diagram you can see that point w lies on the interior of an angle, then

m∠uvx=m∠uvw+m∠wvx.

answer: correct choice is b.

part b.

substitution property of equality:

if x = y, then x can be substituted in for y in any equation, and y can be substituted for x in any equation.

given that xy≅yz and xy=4a+4, yz=20, you can substitute instead of xy the expression 4a+4 and instead of yz the expression 20 into the iquality xy≅yz and obtain

4a+4=20

answer: correct choice is a.