[tex]\it\ \ Fie\ \ d=distan\c{\it t}a\ din\ prima\ parte;\ \ t= timpul\ din\ prima\ parte.\\ \\ v=\dfrac{d}{t} \Rightarrow 4=\dfrac{d}{t}\Rightarrow d=4t\ \ \ \ \ \ (1)\\ \\ Din\ enun\c{\it t},\ avem:\\ \\ d+1,5=\ distan\c{\it t}a\ din\ a\ doua\ parte;\ \ 4-t=\ timpul\ din\ a \ doua\ parte.\\ \\ d+1,5=3(4-t) \Rightarrow d+1,5=12-3t\Big|_{-1,5}\Rightarrow d=10,5-3t\ \ \ \ \ \ (2)[/tex]
[tex]\it (1),\ (2) \Rightarrow 4t=10,5-3t\Big|_{+3t}\Rightarrow7t=10,5\Big|_{:7}\Rightarrow t=1,5h\ \ \ \ \ (3)\\ \\ (1),\ (3)\Rightarrow d=4\cdot1,5\Rightarrow d=6km[/tex]
Prin urmare, lungimea totală a drumului este:
6 + 6 + 1,5 = 13,5km .
