Question 731542
Are rates such as those really uniform?  That's suspicious.


Anyway, let the rates in degrees per minute b e{{{ m = 15/24}}}, and {{{m+n =15/6}}}, so we do not know rate n.  We are expected to assume that when both heaters operate together, the rates are simply summed.  We would do this:


m + n = BOTH-TOGETHER
{{{15/24+n=15/6}}}
{{{n=15/6-15/24}}}
{{{n=(15/6)(4/4)-15/24}}}
You can finish from here.