PHP extension mbstring is missing from your system

Question

I am getting this error.

laravel/framework v5.4.9 requires ext-mbstring * -> the requested PHP extension mbstring is 
missing from your system.

So I followed this: https://stackoverflow.com/a/49087941/14505740 And used

sudo apt-get install php-mbstring 

But I am still getting the same error when I run composer install I am using laravel 5.4 and PHP 7.2.34