how do you find the answer for 5/16 +3/35=

The least common multiple of 16 and 35 is 560. You must convert the fractions to that denominator before adding numerators. You could also add the decimal versions of the fractions, but they go on forever.

5/16 + 3/35 = 175/560 + 48/560
= 223/560 = 0.398214286...