Answer:
b = 6units
Explanation:
You can try to flip the image in the other directions to make the height equals to 10unit. As given that the area of parallelogram is A = b×h so, you can just substitute the "given value" into the foemula :
A = 60units²
h = 10units
60 = b × 10
10b = 60
b = 60/10
= 6units