quãng đường ôtô đi 15' là:
60*15/60=15(km)
quãng đường còn lại là :
135-15=120(km)
thời gian 2 xe gặp nhau là:
120:90=4/3(giờ)
địa điểm 2 xe gặp nhau cách B số km là:
30*4/3=40(km)
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