How do i identify terms and like terms

What is the result of adding the system of equations? 2x+y=4 3x-y=6

Given the two similar triangles, how do i find the missing length? if a=4, b=5, and b'=7.5 find a'

What is the next step in the given proof? choose the most logical approach. a. statement: m 1 + m 2 + 2(m 3) = 180° reason: angle addition b. statement: m 1 + m 3 = m 2 + m 3 reason: transitive property of equality c. statement: m 1 = m 2 reason: subtraction property of equality d. statement: m 1 + m 2 = m 2 + m 3 reason: substitution property of equality e. statement: 2(m 1) = m 2 + m 3 reason: substitution property of equality