Answer:
Let the Dulcina's collection be 'x'
Let the Tremaine collection be 'x-39'
x + x - 39 =129
2x = 129 +39
2x = 168
x = 168/2
x = 84
Dulcina's collection = x = 84
Tremaine's collection = x - 39 = 84 - 39 = 45
as a fraction the answer is
x=(10/9)
as a mixed number
x=1(1/9)
as a decimal
x=1.1
I wasn't sure which form you were looking for I I gave you them all
Brandon is not correct because he should have added 6 negative unit tiles to isolate the variable in step 2—— the answer would have been x=-1
6 times 12 is 72 so 14 times 12 would be 168 if that is what you are looking for. So for that y=168 :-)