Explicație pas cu pas:
9x+5y=60 =>5y=60-9x => 5y=3(20-3x)=>3|5y
=> 3|y cum y-prim => y=3
9x+15=60 =>9x=45=>x=5 prim
7x-4y=49=>4y=7x-49=>4y=7(x-7)=>7|4y =>
7| y cum y prim => y=7
7x-28=49=>7x=77=>x=11 prim
8x+3y=63=>8x=63-3y=>8x=3(21-y)=>3|8x =>
3| x cum x prim => x=3
24+3y=63=>3y=39=>y=13 prim