5 trumpet players
let s represent saxophone players and t trumpet players
thus t = s - 10 → ( 10 less than saxophone players)
also s = 3t = 3( s - 10)
solve s = 3( s - 10)
s = 3s - 30
subtract s from both sides of the equation
0 = 3s - s - 30
0 = 2s - 30
add 30 to both sides
30 = 2s
divide both sides by 2
= s ⇒ s = 15
number of trumpet players = 15 - 10 = 5