[tex]\displaystyle\bf\\2^{31}+2^{30}+2^{29}=x \cdot 2^{28}\\\\2^{28+3}+2^{28+2}+2^{28+1}=x \cdot 2^{28}\\\\2^{28}\cdot2^3+2^{28}\cdot2^2+2^{28}\cdot2^1=x \cdot 2^{28}\\\\2^{28}\Big(2^3+2^2+2^1\Big)=x\cdot 2^{28}\\\\2^{28}\Big(8+4+2\Big)=x\cdot 2^{28}\\\\2^{28}\cdot14=x\cdot 2^{28}~~~\Big|:2^{28}\\\\14=x\\\\\boxed{\bf x=14}[/tex]
