Question Number 22657 by *D¬ B£$T* last updated on 21/Oct/17
$${A}\:{real}\:{image}\:\mathrm{3}\:{times}\:{the}\:{size}\:{of}\:{the}\: \\ $$$${object}\:{formed}\:{by}\:{a}\:{concave}\:{mirror} \\ $$$${on}\:{a}\:{screen}.\:{later}\:{both}\:{the}\:{object}\: \\ $$$$\&\:{the}\:{screen}\:{are}\:{shifted}\:{untill}\:{the} \\ $$$${image}\:{formed}\:{is}\:\mathrm{6}\:{times}\:{the}\:{size} \\ $$$${of}\:{the}\:{object}.\:{if}\:{the}\:{distnce}\:{moved} \\ $$$${is}\:\mathrm{15}{cm}.\:{calculate}\:{the}\:{focal}\:{length} \\ $$$${of}\:{the}\:{mirror}. \\ $$