we know that
area larger triangle (DEF)=[scale factor]²*area smaller triangle (ABC)
solve for scale factor
scale factor=√[area larger triangle/area smaller triangle]
scale factor=√[144/100]------> scale factor=1.2
therefore
measure EF=scale factor *measure BC
solve for measure BC
measure BC=measure EF/scale factor-------> 15/1.2------> 12.5 cm
the answer is
measure BC is 12.5 cm
