The distance between $A$ and $B$ is $3$ km. A cyclist starts from $A$ towards $B$ at $v_1=27$ km/h. At the same time, another cyclist starts from $B$ and travels towards $A$ at $18$ km/h. After what time do they meet? How far is the meeting from $A$?
If $t=x$, then $s_1=27x$ and $s_2=18x$.
$s_1+s_2=3$; $27x+18x=3$; $x=\dfrac{3}{45}=\dfrac{1}{15}$ hours.
Is this the right answer?
Almost. You forgot the time unit (hour). And it would have been better if you had simplified the answer, getting $\frac1{15}$ hours (or 4 minutes).