Grammar is
S$\rightarrow$Ax|By
A$\rightarrow$ By|Cw
B$\rightarrow$ x|Bw
C$\rightarrow$ y
Now observe that what strings these productions are generating
C$\rightarrow$ y is generating only y.
B$\rightarrow$ x|Bw is generating x, xw, xww, xwww, ... That is xw*.
A$\rightarrow$ By|Cw is generating xw*y+yw.
S$\rightarrow$ Ax|By is generating (xw*y+yw)x+xw*y .
That is regular expression for given grammar.