Answer:
16cm
Explanation:
x + x + 3 + x + 7 = 37 (make all sides equal 37)
3x + 10 = 37 (Add x's and coefficiants together)
-10 -10 (subtract 10 from each side)
3x = 27 (divide 27 by 3)
x = 9 (answer)
x, x + 3, x + 7 (finding longest length)
9, 9 + 3, 9 + 7 (Substitute 9 for x)
9cm, 12cm, 16cm (add each together)
16cm (answer)