39 because 6/3= 2 and 78/39 also = 2
Substract 6 to both sides and you get 36 =-2d then you use the multiplicative inverse and d=-18.
28 because we are talking about TENS meaning there can only be 2 digits
4x-2+1=3x+5
Subtract 3x from both sides
x-2+1=5
Same as
x-1=5
Add 1 to both sides
x=6
