I1.1 There are $a$ camels in a zoo. The number of one-hump camels exceeds that of two-hump camels by 10 . If there have 55 humps altogether, find the value of $a$.

I1.3 Let $C$ be a positive integer less than $\sqrt{b}$. If $b$ is divided by $C$, the remainder is 2 ; when divided by $C+2$, the remainder is $C$, find the value of $C$.
11.4 A regular $2 C$-sided polygon has $d$ diagonals, find the value of $d$.

I1.2 If $\operatorname{LCM}(a, b)=280$ and $\operatorname{HCF}(a, b)=10$, find the value of $b$.
Suppose there are $x$ one-hump camels, $y$ two-hump camels.
$$
\begin{array}{l}
x-y=10 \ldots \ldots \ldots . . \\
x+2 y=55 \ldots \ldots . .
\end{array}
$$
$$
\begin{array}{l}
\text { (2) - (1) } 3 y=45 \Rightarrow y=15 \\
\text { sub. } y=15 \text { into (1): } x-15=10 \Rightarrow x=25 \\
a=x+y=25+15=40 \\
C$ divisor !!!)
The number of diagonals of a convex $n$-sided polygon is $\frac{n(n-3)}{2}$.
$$
d=\frac{8 \times 5}{2}=20
$$

Remark: The following note was put at the end of the original question:
(註：對角線是連接兩個不在同一邊上的頂點的直線。)
(NB: a diagonal is a straight line joining two vertices not on the same side.)
The note is very confusing. As the definition of diagonal is well known, there is no need to add this note.
$$
\begin{array}{l}
\mathrm{HCF} \times \mathrm{LCM}=a b \\
2800=40 b \\
b=70
\end{array}
$$