(i) 145

Given octal number: $(145)_8$

To convert to decimal, we multiply each digit by the positional value ($8^n$) where $n$ is the position number starting from 0 on the right.

Calculation:

$$1 \times 8^2 + 4 \times 8^1 + 5 \times 8^0$$ $$= 1 \times 64 + 4 \times 8 + 5 \times 1$$ $$= 64 + 32 + 5$$ $$= 101$$

Therefore, $(145)_8 = (101)_{10}$.

(ii) 6760

Given octal number: $(6760)_8$

Calculation:

$$6 \times 8^3 + 7 \times 8^2 + 6 \times 8^1 + 0 \times 8^0$$ $$= 6 \times 512 + 7 \times 64 + 6 \times 8 + 0 \times 1$$ $$= 3072 + 448 + 48 + 0$$ $$= 3568$$

Therefore, $(6760)_8 = (3568)_{10}$.

(iii) 455

Given octal number: $(455)_8$

Calculation:

$$4 \times 8^2 + 5 \times 8^1 + 5 \times 8^0$$ $$= 4 \times 64 + 5 \times 8 + 5 \times 1$$ $$= 256 + 40 + 5$$ $$= 301$$

Therefore, $(455)_8 = (301)_{10}$.

(iv) 10.75

Given octal number: $(10.75)_8$

This number contains both integer and fractional parts.

Integer Part (10):

$$1 \times 8^1 + 0 \times 8^0$$ $$= 8 + 0 = 8$$

Fractional Part (.75):

$$7 \times 8^{-1} + 5 \times 8^{-2}$$ $$= 7/8 + 5/64$$ $$= 56/64 + 5/64$$ $$= 61/64$$ $$= 0.953125$$

Total:

$$8 + 0.953125 = 8.953125$$

Therefore, $(10.75)_8 = (8.953125)_{10}$.