<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _call(self, x, out=None):
 """Linearly combine ``x`` and write to ``out`` if given."""

        if out is None:
            out = self.range.element()
        out.lincomb(self.a, x[0], self.b, x[1])
        return out