we know the width of the first picture, is 4
we know the ratio from smaller to larger is 1.5:2
thus [tex]\bf \cfrac{\textit{width of small}}{\textit{width of large}}\qquad 1.5:2\implies \cfrac{1.5}{2}=\cfrac{w}{4}[/tex]
solve for "w".
we know the length of the first picture, 6
[tex]\bf \cfrac{\textit{length of small}}{\textit{length of large}}\qquad 1.5:2\implies \cfrac{1.5}{2}=\cfrac{L}{6}
[/tex]
solve for "L".