If -84 is less-than (<) 7c, then 7c must be higher in value than -84.
So 7 multiplied by what = -84? Using a calculator, trial and error, or by dividing -84 by 7, you will find that
7 * (-12) = -84
So your answer is: 'c is more than -12' OR 'c > -12' as any number higher in value than -12 could equal c.
Hope this helps!