Suggest a universal set for the set $\mathrm{C}=\{1,4,9,16,\dots ,100\}$.

If $\mathrm{U}=\left\{\text{natural numbers less than} 50\right\}$, $\mathrm{B}=\left\{\text{multiples of }3\text{ less than }50\right\}$ and $\mathrm{C}=\left\{x\right|x+7\le 8\}$, find ${\mathrm{B}}^{\text{'}}$.

If $\mathrm{U}=\left\{\text{natural numbers less than} 50\right\}$, $\mathrm{B}=\left\{\text{multiples of }3\text{ less than }50\right\}$ and $\mathrm{C}=\left\{x\right|x+7\le 8\}$, find ${\mathrm{C}}^{\text{'}}$.

If $\mathrm{U}=\left\{\text{natural numbers less than} 50\right\}$, $\mathrm{B}=\left\{\text{multiples of }3\text{ less than }50\right\}$ and $\mathrm{C}=\left\{x\right|x+7\le 8, x\in N\}$, check whether $\mathrm{B}\leftrightarrow \mathrm{C}?$

If $\mathrm{U}=\left\{\text{natural numbers less than} 50\right\}$, $\mathrm{B}=\left\{\text{multiples of }3\text{ less than }50\right\}$ and $\mathrm{C}=\left\{x\right|x+7\le 8\}$, find $n\left({\mathrm{C}}^{\text{'}}\right)$.

If $\mathrm{U}=\left\{\text{natural numbers less than} 50\right\}$, $\mathrm{B}=\left\{\text{multiples of }3\text{ less than }50\right\}$ and $\mathrm{C}=\left\{x\right|x+7\le 8\}$, find $n\left({\mathrm{B}}^{\text{'}}\right)$.

If $n\left(\mathrm{U}\right)=60, n\left(\mathrm{A}\right)=15, n\left(\mathrm{B}\right)=38$, find $n\left({\mathrm{A}}^{\text{'}}\right)$ and $n\left({\mathrm{B}}^{\text{'}}\right)$.

If $A=\{4,5,6\}$ and $B=\{x;x\in W\text{ and }x<5\},$ find $A\cup B$.

If $A=\{4,5,6\}$ and $B=\{x:x\in W\text{ and }x<5\},$ find $A\cap B$.