What is the difference between solving systems of equations using substitution, elimination, and graphing?

Acompany is making new soccer uniforms for a team. the company uses 2.5 yards of fabric for each shirt. the company uses 82.5 yards of fabric to make shirts and shorts for 15 players. the equation and solution below represents the situation. 15(2.5+x)=82.5; x=3 what does the solution, x=3, represent?

Ican figure out 20 shares multiply by $117.98 =2359.6920 shares multiply by $124.32=2486.40then take 40 shares multiply by $128.48=5139.20after that i'm lost any be greatly appreciated.

Yesterday i ran 5 miles. today, i ran 3.7 miles. did my percent increase, decrease or is it a percent error? plz i need