$\text{a)}1,3\cdot 10000000=1,3\cdot {10}^7$

$\text{b)}0,58\cdot 100000=0,58\cdot {10}^5=5,8\cdot {10}^4$

$\text{c)}12,4\cdot 100000000=12,4\cdot {10}^8=1,24\cdot {10}^9$

$\text{d)}0,0024\cdot 1000000=0,0024\cdot {10}^6=2,4\cdot {10}^3$

$\text{e)}10,2\cdot {10}^5=1,02\cdot {10}^6$

$\text{f)}235\cdot {10}^7=2,35\cdot {10}^9$

$\text{g)}3000\cdot {10}^4=3\cdot {10}^7$

$\text{h)}0,0012\cdot {10}^9=1,2\cdot {10}^6$

$\text{i)}0,00001\cdot 100000=0,00001\cdot {10}^5=0,01\cdot {10}^2=1\cdot {10}^1$