gimana cara kerjanya???

PQ = ((AB×CQ) + (CD×QB)) ÷ CQ+QB
13 = ((AB×4) + (10×6)) ÷ (4+6)
13 = (4AB + 60) ÷ (10)
13×10 = 4AB+60
130 = 4AB+60
130 - 60 = 4AB
70 = 4AB
70 ÷ 4 = AB
17,5 = AB
jadi panjang AB = 17,5cm