Question 27918
You can let x = the length of the short side. Then the length of next largest side would be x+2 and the length of the largest side would be x+4.  These sides add up to 195 mm.  You can set up the equation to find x, the length of the short side.

{{{x + (x+2) + (x+4) = 195}}} Simplify and solve for x.
{{{3x+6 = 195}}} Subtract 6 from both sides of the equation.
{{{3x = 189}}} Divide both sides by 3.
{{{x = 63}}}

The length of the short side is 63 mm
The length of the middle side is x+2 = 63+2 = 65 mm
The length of the long side is x+4 = 63 + 4 = 67 mm

Check: 63+65+67 = 195 mm