Generally, in theory, echo $a + $b will give the answer to the question, or to be more specific then:

0.1 + 0.7 === 0.8 // false

why?

the answer is not obvious but: 0.1 + 0.7 = 0.7999999999999999

Your arithmetic of equally — floating exact not exact, round to a couple of digits after the jam with the aid number_format then everything will work correctly