Operations with scientific notation (ACT). Game on.

Multiply coefficients and add exponents: $5 \cdot 4 = 20$ and $-3+(-2)=-5$, giving $20 \times 10^{-5}$. Rewrite $20=2 \times 10^{1}$, so $2 \times 10^{1} \times 10^{-5}=2 \times 10^{-4}\textsf{.}$

Divide coefficients and subtract exponents: $6.3 \div 2.1 = 3$ and $-4-(-9)=5$. So the quotient is $3 \times 10^{5}\textsf{.}$

Multiply coefficients and add exponents: $4 \cdot 5 = 20$ and $3+4=7$, giving $20 \times 10^{7}$. Rewrite as $2 \times 10^{1} \times 10^{7}=2 \times 10^{8}\textsf{.}$

Divide coefficients and subtract exponents: $9 \div 3 = 3$ and $-6-2=-8$. So $\dfrac{9 \times 10^{-6}}{3 \times 10^{2}}=3 \times 10^{-8}\textsf{.}$

Multiply coefficients and add exponents: $2.5 \cdot 4 = 10$ and $6+(-3)=3$, giving $10 \times 10^{3}$. Rewrite as $1 \times 10^{1} \times 10^{3}=1 \times 10^{4}\textsf{.}$

Divide coefficients and subtract exponents: $3 \div 6 = 0.5$ and $5-2=3$, giving $0.5 \times 10^{3}$. Rewrite as $5 \times 10^{-1} \times 10^{3}=5 \times 10^{2}\textsf{.}$

Divide coefficients and subtract exponents: $7.2 \div 1.2 = 6$ and $-5-(-2)=-3$. So the quotient is $6 \times 10^{-3}\textsf{.}$

Multiply coefficients and add exponents: $1.5 \cdot 8 = 12$ and $4+3=7$, giving $12 \times 10^{7}$. Rewrite as $1.2 \times 10^{1} \times 10^{7}=1.2 \times 10^{8}\textsf{.}$