Question

the cost of 3 kg of sugar is 105 rupees what will be the cost of 15 kg of sugar

Answer 1

cost of 1 kg =  105 /3 = 35 
so cost of 15 kg =rs 35 * 15= rs 525

Answer 2

See here cost of3kg sugar is rs 105. To find cost of 15kg sugar 3kg=105. 15kg =3*5. So now 15kg =105*5. So 15 kg=525