The width of this rectangle is measured as 19.4mm correct to 1 decimal place.
what is the lower bound for the area of the rectangle?

We need to find the shortest possible width and length to get the smallest possible area.
To get the boundaries for 19.4, we go on to the next significant figure (the hundredths) and ± 5 of them.
The boundaries are, therefore: 19.35 - 19.45
As for the length, we can see they've added 5 units as the measurement is correct to 2 sig' figures, which is the tens.
And so, if we do as we did before, we go to the next sig' figure (the units) and ± 5 of them, we get the boundaries to be 365 - 375.

Now, we just multiply the lower bounds of the length and width to get the minimal/lower-bound area:
365 * 19.35 = 7062.75 mm²