To find perimeter $ P $ use formula:
$$ P = 2 a + 2 b $$After substituting $a = 7\, \text{cm}$ and $b = 7\, \text{cm}$ we have:
$$ P = 2 \cdot 7\, \text{cm} + 2 \cdot 7\, \text{cm} $$ $$ P = 14\, \text{cm} + 14\, \text{cm} $$ $$ P = 28\, \text{cm} $$