Question 131551
a + 3a= 1a = 3a = (1 + ?) a


This doesn't make any sense as you have written it.  I suspect you weren't very careful with your typing and you really meant:


 {{{a + 3a= red(1a + 3a) = (1 + x) a}}}  Makes more sense. (I replaced your question mark with an x so that the formula would render properly)


The question mark (or x) needs to be replaced with a 3.