I an:x/4
x-x/4=3x/4
II an:60/100·3x/4=18x/40
3x/4-18x/40=12x/40
III an:12x/40=72
x=72·40/12
x=240 km lungimea autostrazii
verificare: Ian:240-240/4=180
IIan:180·60%=108
180-108=72
b) Ian a construit 240/4=60km
IIan:108
240km--------------------3.000.000.000
60+108=168------------x
x=168·3.000.000.000/240
x=2.100.000.000 deci 2100 milioane lei