Let N be the amount of lbs of lettuce. The proportion 6.3:4.5 must be the same as N:8.5. Then:
[tex]\frac{N}{8.5}=\frac{6.3}{4.5}[/tex]Solve for N:
[tex]N=\frac{6.3}{4.5}\times8.5=11.9[/tex]Then, if there are 8.5 lbs of tomatoes, there must be 11.9 lbs of lettuce.
The answer is: 11.9