To find side $ a $ use Law of Cosines:
$$ a^2 = b^2 + c^2 - 2 \cdot b \cdot c \cdot \cos( \alpha ) $$After substituting $b = \frac{ 39 }{ 5 }$, $c = \frac{ 28 }{ 5 }$ and $\alpha = 35^o$ we have:
$$ a^2 = \left(\frac{ 39 }{ 5 }\right)^2 + \left(\frac{ 28 }{ 5 }\right)^2 - 2 \cdot \frac{ 39 }{ 5 } \cdot \frac{ 28 }{ 5 } \cdot \cos( 35^o ) $$ $$ a^2 = \frac{ 1521 }{ 25 } + \frac{ 784 }{ 25 } - 2 \cdot \frac{ 39 }{ 5 } \cdot \frac{ 28 }{ 5 } \cdot \cos( 35^o ) $$ $$ a^2 = \frac{ 461 }{ 5 } - 2 \cdot \frac{ 1092 }{ 25 } \cdot \cos( 35^o ) $$ $$ a^2 = \frac{ 461 }{ 5 } - \frac{ 2184 }{ 25 } \cdot 0.8192 $$ $$ a^2 = \frac{ 461 }{ 5 } - 71.5611 $$ $$ a^2 = 20.6389 $$ $$ a = \sqrt{ 20.6389 } $$$$ a \approx 4.543 $$