Given the following why is $($d$)$rorrert please explain the green answer to $d_{{?}_{?}}$ in the image

$($b$)$ Write a variant for the alstract syntax of this language.

$($c$)$ Formally define the big step semantics of this language.

$\frac{\text{v}\text{i}\text{n}\text{Z}}{v!tv}$ Num

$\frac{E_{1}1-t_1(x,t_3,E_2),E_{1}1-t_2{v}_1,E_2[x{v}_1]+t_3{}_2}{E_1+t_1{t}_2{v}_2}$ CALL.

$\frac{E1-t_1||v_1,E-t_1{}_2}{E-t_1+t_2{v}_1+t_2}$ADD

$\frac{E\text{:}-t_1{v}_{1}EP-t_1{v}_2}{B-t_1-t_2{v}_1-v_2}$ SUB

$($d$)$ Write an evaluator for this language based on your big step semantics.

defun eval $Et$

match $t$ with

case $m(n)n$

case Var$(x)E(x)$

case FuncExpr$(v,t)(FuncExpr(v,t),E)$

case BopExpr$(x,b,y)$

let

xlarrevalEx

ylarrevalEy

in

match $b$ with

case Add $x+y$

case Sub $x-y$

case $l{x}^{**}y$

case Div $\frac{x}{y}$

case CallExpr$(f,x)$

match $,$ eval $Ex$ with

case $((FuncExpr(v,t),E),x)$

eval $E[v|x]t$

otherwise ERROR