va rog ajutați-ma urgent

x/y=5/13
a)(x+y)/y=x/y+1=5/13+1=(5+13)/13=18/13
b)x/(y+x)=1/(y/x+1)=1/(13/5+1)=5/18
c)(y-x)/x=y/x-1=13/5-1=(13-5)/5=8/5