The answer is: mass of the snack mix can you consume and still be within the FDA limit is 491 grams.
ω(Na) = m(Na) ÷ m(salt).
ω(Na) = 39.33 g ÷ 100 g.
ω(Na) = 0.3933; mass percentage of sodium in salt.
m(salt) = 2.4 g ÷ 0.3933.
m(salt) = 6.10 g; mass of salt recommended for consumation.
Make proportion: 1.24 g : 100 g = 6.10 g ÷ m(mix).
m(mix) = 491.93 g; mass of the snack mix.