Ah ok The property is
"The Addition Property of Equality"
Answer:
a=7
Step-by-step explanation:
6a-42=-7a+49
(add 7a to 6a)
13a-42=49
(add 42 to 49)
13a=91
(divide 91 by 13)
a=7
45=1,3,5,9,15,45
37=only 1 and 37 because it is prime.
51= 1,3,17,51
It should be -1 I believe.