Explanation:
Emma = Alex - 5
Alex = Toni × 3
therefore,
Toni = Alex / 3
Emma + Alex + Tony = 93
so, let's use the first two equations (identities) in the last big one, so that we have actually only one variable (Alex).
once we solve that, we can get the other two values out of the first 2 equations.
(Alex - 5) + Alex + (Alex/3) = 93
let's multiply everything by 3 to get rid of the fraction :
3(Alex - 5) + 3×Alex + 3(Alex/3) = 3×93
3×Alex - 15 + 3×Alex + Alex = 279
7×Alex - 15 = 279
7×Alex = 294
Alex = 294/7 = 42 runs.
Emma = Alex - 5 = 42 - 5 = 37 runs.
Toni = Alex/3 = 42/3 = 14 runs.