Expression Calculated Missing

s$[]\text{'}$W$\text{'}$

$6$

$[2]\text{'}$C$\text{'}$

s

s$[4$:$]\text{'}$o Wo$\text{'}$

$8$

s$[$:$]\text{'}$He$\text{'}$

$2$

s$[$:$]\text{'}$rld$!\text{'}$

$8$

$[2$:$100]\text{'}$a$\text{'}$

error

$[3$:$1]\text{'}\text{'}$

error

s$[1$:$2+]$ 'ello'

$3$:$6$

$[-2]\text{'}$b$\text{'}$

s

s$[-]\text{'}$H$\text{'}$

$12$

s$[$:$-3]\text{'}$or$\text{'}$

$7$

$[-2$:$]\text{'}$bc$\text{'}$