Explicație pas cu pas:
a) 2x + 10 < 10 => 2x < 0 => x < 0 => A = ∅ => card A = 0
b) 2x + 8 < 10 => 2x < 2 => x < 1 => A = {0} => card A = 1
c) 2x + 6 < 10 => 2x < 4 => x < 2 => A = {0, 1} => card A = 2
d) 2x + 4 < 10 => 2x < 6 => x < 3 => A = {0, 1, 2} => card A = 3