0.12 - 0.34x = 0.56 can be simplified by multiplying both sides by 100

12 - 34x = 56

now does that look easier?

Now subtract 12 from both sides

-34x = 44

x = -44/34

x = -22/17

Obviously we could have solved it using the original values, but this method can reduces the chance of error.

Now, to double check it;

0.12 - 0.34(-22/17) =? 0.56

-0.34(-22/17) =? 0.44

(34/100)(22/17) =? 0.44

(44/100) = 0.44

Yes, it checks

12 - 34x = 56

now does that look easier?

Now subtract 12 from both sides

-34x = 44

x = -44/34

x = -22/17

Obviously we could have solved it using the original values, but this method can reduces the chance of error.

Now, to double check it;

0.12 - 0.34(-22/17) =? 0.56

-0.34(-22/17) =? 0.44

(34/100)(22/17) =? 0.44

(44/100) = 0.44

Yes, it checks