Question 53476
The three sides of the triangles: 1) x; 2) 3x; and 3) 15 cm.
Their sum, or perimeter, can be no more than 75. So first set up the inequality like this: {{{x+3x+15<=75}}}
From there solve for x, like this:
{{{4x+15<=75}}}     Combined like terms
{{{4x<=60}}}        Subtracted 15 from both sides
{{{x<=15}}}         Divided both sides by 4

To draw this out start with a number line with an OPEN circle similar to this: {{{number_line(300,0,24,15)}}}
Then shade in everything less than 15.
The greatest length the sides could be are 15, 15, and 45.