gary says that 24.3-17.56=6.86. explain what he did wrong?

Question

the gas tank in max's car holds 16 gallons. when hee had the tank filled he got 15.3 gallons how close was the tank to being empty

Answer 1

24.30-17.56=6.74

it had only 0.7 gallon in it

Answer 2

(1)
24∙3 - 17∙56 = 6∙74

24∙3 =24∙30

24∙30
-17∙56
-----------
+ 6∙74
To get an answer of 6∙86, the decimal was add - not subtracted.

(2)
If the tank holds 16 gallons, and it took 15∙3 gallons to fill it, then before filling the tank it contained:
Total volume = Non-used volume + Used volume.
16 gallons = Non-used volume + 15∙3 gallons.
Non-used volume = 16 gallons - 15∙3 gallons.
Non-used volume = 0∙7 gallons.

Answer 3

24.3-17.56=6.74

He filled 15.3 gallons so if there was no fuel at all before, then that's how close the tank is to being empty: 15.3 gallons