#### Answer

$1.26 \times 10^8$

#### Work Step by Step

Multiply 4.2 and 3 together, then multiply the powers of 10 together to obtain:
$=12.6 \times 10^{13+(-6)}
\\=12.6 \times 10^7$
Simplify to put the number in scientific notation.
$=1.26 \times 10^{7+1}
\\=1.26 \times 10^8$