To find side $ a $ use Pythagorean Theorem:
$$ s^2 + \frac{ a^2 }{ 4 } = e^2 $$After substituting $ s = 60 $ and $ e = 4 $ we have:
$$ 60^2 + \frac{ a^2 }{ 4 } = 4^2 $$ $$ \frac{ a^2 }{ 4 } = 4^2 - 60^2 $$ $$ \frac{ a^2 }{ 4 } = 16 - 3600 $$ $$ a^2 = -3584 \cdot 4 $$ $$ a^2 = -14336 $$This equation has no solution $ \Longrightarrow $ The problem has no solution.