Răspuns:
a = 9
Explicație pas cu pas:
28+72÷ a+12=48
fie notam 72÷ a = y
28 + y +12 = 48
28 + 12 + y =48
40+ y = 48
y = 48-40
y = 8
72÷ a = y
72÷ a = 8
a = 72÷ 8
a= 9
28+72÷a+12=48
28+72÷a=48-12
28+72÷a=36
72÷a=36-28
72÷a=8
a=72:8
