Update HOME_EXAM.md

HOME_EXAM.md

@@ -157,7 +157,9 @@ Given a expression $e$ in the state $\sigma$  that evaluates to a value $n$ or b
 
 #### Arithmetic
 Addition:\
-$\frac{\lang e1, \sigma \rang \ \Downarrow \ n1 \; \lang e2, \sigma \rang \ \Downarrow \ n2}{\lang e1 + e2, \sigma \rang \ \Downarrow \ n1 + n2}$
+```math
+\frac{\lang e1, \sigma \rang \ \Downarrow \ n1 \; \lang e2, \sigma \rang \ \Downarrow \ n2}{\lang e1 + e2, \sigma \rang \ \Downarrow \ n1 + n2}
+```
 
 Subtraction:\
 $\frac{\lang e1, \sigma \rang \ \Downarrow \ n1 \; \lang e2, \sigma \rang \ \Downarrow \ n2}{\lang e1 - e2, \sigma \rang \ \Downarrow \ n1 - n2}$