Answer:
[tex]\large\boxed{V=Bh,\ 26x=B(6.5)\to B=4x}[/tex]
Step-by-step explanation:
[tex]\text{The formula of a volume of cylinder:}\\\\V=Bh\\\\\text{We have}\ V=26x\ m^3\ \text{and}\ h=6.5\ m.\\\\\text{Substitute:}\\\\26x=B(6.5)\qquad\text{divide both sides by 6.5}\\\\\dfrac{26x}{6.5}=B\to B=4x[/tex]