Ashopper purchased 8 t-shirts and 5 pairs pants for $220. the next day, he purchased 5 t-shirts and 1 pair of pants for $112. how much does each t-shirt and each pair of pants cost?

You can solve this with an equation:
8x+5y=220                    (x represents cost of t-shirt, y represents cost of pants)
5x+y=112
choose an equation and isolate either x or y
ex.) 5x+y= 112
      -5x      -5x

         y=112-5x     
substitute y into the other equation:

8x+5y=220> 8x+5(112-5x)=220
Distribute: 8x+560-25x=220
subtract 560 on both sides: 8x-25x=220-560
8x-25x=-340
combine like terms: -17x=-340
Divide -17 on both sides: -17x=-340
                                           ___
                                         -17      -17
x=20 each t shirt costs $20
plug in x into the other equation to find y: 112-5x=y
substitute x: 112-5(20)=y-->112-100=y
each pair of pants costs $12

the answer is true, euclidean geometry is based on the postulates of Euclid