how to sum 2 numbers in typescript
<p>I have this properties</p>

<pre><code>export interface IOurFirstSpfWebPartWebPartProps {
  description: string;
  n1: number;
  n2: number;

}
</code></pre>

<p>Then I have this method</p>

<pre><code>public render(): void {
    this.domElement.innerHTML = `
      &lt;div class="${styles.ourFirstSpfWebPart}"&gt;
        &lt;div class="${styles.container}"&gt;
          &lt;div class="ms-Grid-row ms-bgColor-themeDark ms-fontColor-white ${styles.row}"&gt;
            &lt;div class="ms-Grid-col ms-u-lg10 ms-u-xl8 ms-u-xlPush2 ms-u-lgPush1"&gt;
              &lt;span class="ms-font-xl ms-fontColor-white"&gt;Welcome to SharePoint!&lt;/span&gt;
              &lt;p class="ms-font-l ms-fontColor-white"&gt;Customize SharePoint experiences using Web Parts.&lt;/p&gt;
              &lt;p class="ms-font-l ms-fontColor-white"&gt;${this.properties.n1} + ${this.properties.n2}&lt;/p&gt;
              &lt;a href="https://github.com/SharePoint/sp-dev-docs/wiki" class="ms-Button ${styles.button}"&gt;
                &lt;span class="ms-Button-label"&gt;Learn more&lt;/span&gt;
              &lt;/a&gt;
            &lt;/div&gt;
          &lt;/div&gt;
        &lt;/div&gt;
      &lt;/div&gt;`;
  }
</code></pre>

<p>However this is printing 1+2 instead of 3.</p>