Use the exponent rules to simplify in exponential form.

$$
7^{12-4}
$$

$$
7^8
$$
The simplified form is $\boxed{7^8}$.

$$
9^{8-6}
$$

$$
9^2
$$
The simplified form is $\boxed{9^2}$.

$$
12^{7-3}
$$

$$
12^4
$$
The simplified form is $\boxed{12^4}$.

$$
y^{8-4}
$$

$$
y^4
$$
The simplified form is $\boxed{y^4}$.

$$
8^{6 \times 2}
$$

$$
8^{12}
$$
The simplified form is $\boxed{8^{12}}$.

$$
9^{12 \times 4}
$$

$$
9^{48}
$$
The simplified form is $\boxed{9^{48}}$.

$$
a^{5 \times 3}
$$

$$
a^{15}
$$
The simplified form is $\boxed{a^{15}}$.

$$
p^{2 \times 2}
$$

$$
p^4
$$
The simplified form is $\boxed{p^4}$.

$$
2 \times a^{10 \times 3}
$$

$$
2a^{30}
$$
The simplified form is $\boxed{2a^{30}}$.

$$
3^2 \times y^{4 \times 3}
$$

$$
3^2 y^{12}
$$

$$
9y^{12}
$$
The simplified form is $\boxed{9y^{12}}$.

$$
(-4)^3 = -4 \times -4 \times -4 = -64
$$

$$
(3^2)^3 = (9)^3 = 9 \times 9 \times 9 = 729
$$

$$
-64 + 729 = 665
$$
The value is $\boxed{665}$.

$$
3^{4-3} = 3^1 = 3
$$

$$
\sqrt{8} = \sqrt{4 \times 2} = \sqrt{4} \times \sqrt{2} = 2\sqrt{2}
$$

$$
3 + 2\sqrt{2}
$$
The value is $\boxed{3 + 2\sqrt{2}}$.

$$
4^2 = 16
$$
$$
4^1 = 4
$$
$$
4^0 = 1
$$

$$
16 + 4 + 1 = 21
$$
The value is $\boxed{21}$.

$$
3^{10-5-2}
$$

$$
3^{5-2} = 3^3
$$

$$
3^3 = 3 \times 3 \times 3 = 27
$$
The value is $\boxed{27}$.

$$
10^{2+1+0} = 10^3
$$

$$
10^3 - 10^3 = 0
$$
The value is $\boxed{0}$.