10^15*10^7/10^19=10^22/10^19=10^3=1000

7^8/7*7^7=7^8/7^8=1

(-3)^5*(-3)^3/(-3)^7=(-3)^8/(-3)^7=-3

(0.2)^8*(0.2)^2/(0.2)^4*(0.2)^3=(0.2)^10/(0.2)^7=(0.2)^3=0.008