For the natural numbers \( m,n \), if \( (1-y)^{m}(1+y)^{n}=1+a_{1}y+a_{2}y^{2}+\ldots +a_{m+n}y^{\,m+n} \) and \( a_{1}=a_{2}=10 \), then the value of \( m+n \) is equal to:
\( 100 \)
\( 80 \)
\( 64 \)
\( 88 \)