Răspuns:
(a,b)∈{(9,3), (8,2), (7,1)}
Explicație pas cu pas:
4a+3b=42, a,b∈{0,1,...,9}
3a+4b numar perfect
4a+3b=3a+4b+a-b=42
a-b<10, a-b = 42 - (3a+4b)
3a+4b ∈ {36}, ⇒a-b=42-36=6,
variante posibile: a-b= 6 = 9-3 = 8-2 = 7-1
⇒(a,b)∈{(9,3), (8,2), (7,1)}