You have to find cos(x) from sin(x) =4/5, which would be:cos(x) =3/5. Then;
You have to find cos(y) from sin(y) =5/13, which would be:cos(y) =12/13. Then:
You have to use this formula: sin(x + y) = sin x cos y + cos x sin y=4/5*12/13 + 3/5*5/13 =63/65
+79 
