2019/007) Show that if $34x = 43 y$ then x + y is not a prime

if $34 x = 43 y$
then $34x + 34 y = 77 y$
or $34(x+y) = 77 y$
as 77 and 34 are co primes so 77 is divisor of x +y and hence x+y is a multiple of 77. even if it is 77 it is not a prime
so x + y is not a prime