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)
pootis
6,12,18,24,30,36,42,48,54,60,66,72,78,84,90,96,102