ERROR TypeError: co.Number is not a function

I am trying to multiply two strings with Angular.

<h5>{{Number(someString) * Number(someOtherString)}}</h5>

but I am getting this error:

ERROR TypeError: co.Number is not a function

How can I multiply two strings with Angular in the HTML?

Edit:

gsc pointed out that I can simply multiply the strings together.

{{'4'*'3'}}

12

However, be careful

{{'4'+'3'}}

43