a) a*b=624
(a+10)*b=864
impartim cele 2 ecuatii:
(a+10)*b/a*b=864/624
simplificam cu b
(a+10)/a=864/624
864a=624a+6240
240a=6240 => a=6240/240 => a=26
26*b=624 => b=624/26 => b=24
b) a*b=3450
(a-20)*b=1950
impartim cele 2 ecuatii si simplificam cu b:
a/a-20=3450/1950
1950a=3450a-69000 => 1500a=69000 => a=46
46b=3450 => b=75