Answer:
Its because of PEDMAS.
To solve using that you start with your P which is parentheses. So (7-4) ends up being 3. You can skip the e because there is no exponents. Next letter is D which is division so 12 divided by 3 is 4. Next is M which is Multiplication so 5 x 3 is 15. Finally A is addition so the only terms you have left is 4 and 15 so add those up and you end up with 19! This rule goes for any type of equation like this and it is essential you follow it that way otherwise you will end up solving your problem incorrectly.
