Let S be the first side. Longest side is then 2S. Third side is 2S-10. Perimeter is sum of all three sides = S+2S+2S-10 = 75 => 5S-10=75 5S=75+10=85 S=17
Therefore S=17 is the first side. Longest side is then 2S=2*17=34. Third side is 2S-10=2*17-10=24.