Evaluate YAML elements with ERB syntax

Question

I have a YAML which includes some ERB blocks:

---
- id: "1"
  pre: |
     <%
     a = rand(2..20)
     b = rand(1..20)
     %>
  sentence: "The result of <%=a%> + <%=b%> is <%=a+b%>"
- id: "2"
  pre: |
     <%
     a = rand(1..20)
     b = 5
     %>
  sentence: "The fraction $\frac{<%=a%>}{<%=b%>}$ equals to $<%=Rational(a, b)%>$"
[many more]
---

I want to get element N, evaluate as ERB template and return as YAML string

Example: if we get element 1, I expected to get:

---
- id: "1"
  pre: |

  sentence: "The result of 3 + 4 is 7"
---