It looks like you are using WolframAlpha to try to solve your problem. That is only one of several different products that Wolfram has. People often assume that questions are about other Wolfram products and not about WolframAlpha.
WolframAlpha has limits on how large a problem that it can solve.
There is another online service from Wolfram that you can use to solve your problem. It requires a slightly different notation to get it to understand a problem and provide an answer.
If you open your browser and go to
https://www.wolframcloud.com/objects/b3m2a1/LetMeMathematicaThatForYou.html
and you patiently wait until "Type your Wolfram Language input" appears
and you give one left mouse click in the large white space below that
and then you tap the x key and patiently wait until that appears
and then you tap the backspace key and patiently wait until the x disappears
and then you paste exactly this
Solve[{(o-x)(n-x-y-z)==(a-x-y)(b-x-z),(p-y)(n-x-y-z)==(a-x-y)(c-y-z),(q-z)(n-x-y-z)==(b-x-z)*(c-y-z)},{x,y,z}]
into the large white space and you patiently wait until that appears
and then you press and hold the <shift> key while you tap the <enter> key
and you patiently wait until a box appears that includes "large output"
and you give one left mouse click on "show all"
then in a few moments a warning should show up saying that the result is so large that it wants to ask if you really want to do this or not
and give one left mouse click on "Try rendering anyway"
and in a few seconds a small box will appear saying that it is working on it
and in perhaps a minute several different solutions, each inside { and } should appear.
A few of the solutions are small and simple, but you should be able to see how very large some of the solutions are.
Hopefully this has given you solutions to your problem.