Hello!
To find the volume of a rectangular prism you use the equation
V = lhw
v is volume
l is length
h is height
w is width
Put in the values you know
180 = 6 * 5 * w
Divide both sides by 6
30 = 5 * w
Divide both sides by 5
6 = w
Answer is 6cm
Hope this helps!