Complete Task II: calculations with squares, square roots, simplifying expressions, and solving equations.

$$
3^2 = 9
$$
$$
5^2 = 25
$$

$$
9 + 25 = 34
$$
$$
\boxed{\text{34}}
$$

*b) $\sqrt{49}$

$$
\sqrt{49} = 7
$$
$$
\boxed{\text{7}}
$$

$$
2x + 3 + x - 5
$$

$$
(2x + x) + (3 - 5) = 3x - 2
$$
$$
\boxed{\text{3x - 2}}
$$

*b) $(3x^2 - 2x + 1) - (x^2 + x - 4)$

$$
3x^2 - 2x + 1 - x^2 - x + 4
$$

$$
(3x^2 - x^2) + (-2x - x) + (1 + 4) = 2x^2 - 3x + 5
$$
$$
\boxed{\text{2x^2 - 3x + 5}}
$$

*c) $2(x + 4) - 3(x - 2)$

$$
2x + 8 - 3x + 6
$$

$$
(2x - 3x) + (8 + 6) = -x + 14
$$
$$
\boxed{\text{-x + 14}}
$$

$$
2x + 5 - 5 = 17 - 5
$$
$$
2x = 12
$$

$$
\frac{2x}{2} = \frac{12}{2}
$$
$$
x = 6
$$
$$
\boxed{\text{x = 6}}
$$

*b) $3(x - 2) = 15$

$$
\frac{3(x - 2)}{3} = \frac{15}{3}
$$
$$
x - 2 = 5
$$

$$
x - 2 + 2 = 5 + 2
$$
$$
x = 7
$$
$$
\boxed{\text{x = 7}}
$$