$17\times30=510$ $19\times 24=456$ $510-456=54$ $54\div(30-24)=9$  $510-30\times9=240$ $240+6\times9=294$ $294\div 6=49$ 
A piece of pasture can feed $$17$$ cow for $$30$$ days or $$19$$ cows for $$24$$ days. If the grass grows at the same speed every day, how many cows can it feed for $$6$$ days? ． 
1. $$38$$ 
2. $$45$$ 
3. $$49$$ 
4. $$52$$ 