7.4. Two cyclists set off simultaneously towards each other from points $A$ and $B$ and met 70 km from $A$. Continuing to move at the same speeds, they reached $A$ and $B$ and turned back. They met for the second time 90 km from $B$. Find the distance from $A$ to $B$.
7.4. Answer: 120 km. Let $x$ be the distance from $A$ to $B$. By the first meeting, both cyclists together had traveled $x$ km, and by the second meeting, $-3x$ km. Therefore, the cyclist who started from $A$ had traveled $3 \cdot 70 = 210$ km by the second meeting. On the other hand, he had traveled $x + 90$ km. Thus, $x = 210 - 90 = 120$ km.