Answer:
0.6 miles
Explanation:
We are given that the distance around the lake is 0.75 miles
Derek ran on Monday=0.8 of the distance
We have to find that how far Derek run
0.8 of the distance=

0.8 of the distance=0.6 miles
Derek ran on Monday=0.6 miles
Hence, Derek run on Monday=0.6 miles