Answer:
beginning supplies 1,600
Step-by-step explanation:
With the following identity we will sovle for beginning supplies:
beginning + purchases = ending + expense
the left side are the input of supplies
and the right side are the output
we will plug into the formula and solve for beginning supplies
beg + 3,400 = 900 + 900
beg = 3,400 - 900 - 900 = 1,600