Question 325109
First divide {{{12a+18b}}} by 3 to find the length of one side: {{{(12a+18b)/3=(12a)/3+(18b)/3=4a+6b}}}



So each side is {{{4a+6b}}} units long.



It turns out that any midsegment will be equal to half of the length of one side length (since we're dealing with an equilateral triangle). So the length of QR is {{{(4a+6b)/2=2a+3b}}} units long.