Question 1023593
Hi there,
Make the equal sides = 'x' each
The base = x - 3
Perimeter = two equal sides + base 
36cm = x + x + (x - 3)
Collect like terms:
x + x + (x - 3) = 36
x + x + x - 3 = 36
3x = 36 + 3
3x = 39
x = 13
Two equal sides = 13cm each
Base = 10cm.
Hope this helps :-)