Let the amount of product A bought be x and the amount of product B bought be y, then
x + y = 4,000 . . . (1)
0.1x + 0.04y = 352 . . . (2)
(2) x 10 ⇒ x + 0.4y = 3,520 . . . (3)
(1) - (3) ⇒ 0.6y = 480
y = 480 / 0.6 = 800
From (1), x + 800 = 4,000
⇒ x = 4,000 - 800 = 3,200
Therefore, the store owner bought 3,200 of product A and 800 of product B.