Mr. Knowles' Equilateral Equations puzzle

Created by David Landy (Mar 02, 2018).

Nice simple task using expressions in x and y to represent the angles of an equilateral triangle. Might be a nice warmup problem for many folks. The original version is here: Full resource at : https://www.tes.com/teaching-resource/the-equilateral-triangle-simultaneous-equations-starter-plenary-problem-solving-11810770?theme=1