Answer/Step-by-step explanation:
1.
; 3
Let's solve for a.
(subtraction property of equality)

(division property of equality)


Therefore, 3 is a solution to 9 = 2a + 3
2.
; 7
(- × - = +)
(Subtraction property of equality)

(division property of equality)

Therefore, 7 is not a solution of 
3.
; 1
Therefore, 1 is a solution of
.