To find incircle radius $ r $ use formula:
$$ r = \dfrac{ \sqrt{ 3 } \cdot a }{ 2 } $$After substituting $a = 0.875\, \text{cm}$ we have:
$$ r = \dfrac{ \sqrt{ 3 } \cdot 0.875\, \text{cm} }{ 2 } $$$$ r = \dfrac{ 1.5155\, \text{cm} }{ 2 } $$ $$ r \approx 0.7578\, \text{cm} $$