hbaxhSGGICgjbaJhcbzkcbh m sry it had to be at least 20 characters long

e and c

Step-by-step explanation:

they are across from each other and equal

11. =38420000
Step By Step:
3.9(107)−5.8(105)=(3.9)(10000000)−5.8(105)=39000000−5.8(105)=39000000−(5.8)(100000)=39000000−580000=38420000

12. =2520000
Step By Step: 
6.2(105)+1.9(106)=(6.2)(100000)+1.9(106)=620000+1.9(106)=620000+(1.9)(1000000)=620000+1900000=2520000

13.=999260000000
Step By Step:
 (1012)−7.4(108)=(1)(1000000000000)−7.4(108)=1000000000000−7.4(108)=1000000000000−(7.4)(100000000)=1000000000000−740000000=999260000000

14. =225
Step By Step: 
4.5−10−1=4.5−110=225

7(10−4)=71000
Step by Step:
 7(10−4)=7(110000)=710000

8(10−3)=1125
step by step:
8(10−3)
=8(11000)=1125