2a - 5d = 30 dove for d
i hope this helps you 2a-30= 5dd=2a-30/5d=2a/5-6
2a - 5d = 30 solve for d
subtract 2a to both sides
2a - 5d - 2a = 30 - 2a
simplify
-5d = 30 - 2a
divide both sides by -5
-5d/-5 = (30 - 2a) / -5
d = -6 +0.4a
d = 0.4a - 6