Generated by SassMeister.com.

SassMeister-input.scss

// ----
// libsass (v3.2.5)
// ----

// current way
@function strip-units($number) {
  @return $number / ($number * 0 + 1);
}

// new way
// @function strip-units($number) {
//   @if type-of($number) == 'number' and not unitless($number) {
//     @return $number / ($number * 0 + 1);
//   }
//   @return $number;
// }

@function rem($number, $divisor: 10) {
  @return (strip-units($number ) / strip-units($divisor)) * 1rem;
}

$first-var: rem(10);
$second-var: rem(strip-units($first-var) * 200);

.className {
  border-width: $first-var;
  height: $second-var;
}

SassMeister-output.css

.className {
  border-width: 1rem;
  height: 20rem;
}