Here’s seven triple-simultaneous-equations plus one quadruple-simultaneous-equation. A great extension task for more able students (whilst others consolidate and ensure that they understand regular, two-simulataneous-equations).
Whilst harder, these all have whole number solutions (bar the last triple question) so that students can focus on the maths and proceedures without getting bogged down in numberwork.
Tried and tested in the classroom many times. This download includes a pdf file as well as the original Word file for easy editing.