Since he spent equal amount on each type of food,

a) $1680 ÷ 2 = $840
He spent $840 on each type of food.

$840 ÷ $10 = 84
84 x 3 = 252

He bought 252 packets of cereal.

$840 ÷ $28 = 30
30 x 2 = 60

He bought 60 packets of rice.


b)

Since equal packets of each type of food were bought, we need to make the number of packets the same first.

Cereal : 3 for $10
Rice : 2 for $28

Notice that 3 x 2 = 6 . The lowest common multiple of 3 and 2 is also 6.

So,

Multiply by 2,
Cereal : 3 for $10 → 6 for $20

Multiply by 3 ,
Rice : 2 for $28 → 6 for $84

$84 - $20 = $64

Every 6 packets of rice cost $64 more than every 6 packets of cereal.


$576 ÷ $64 = 9

9 x 6 packets = 54 packets

54 packets of rice cost $576 more than 54 packets of cereal.

Total number of packets bought = 54 x 2 = 108

Thank You, J! I really appreciate your help and time. Have a good day

You are welcome, have a good day too