I made these questions to hopefully reinforce the idea of area as the space inside a shape, rather than just the answer you get when you multiply numbers together. Also I want them to see why the area of the triangle is half the area of the rectangle which it is enclosed within. I made them using this Geogebra file but then pasted a few to make this worksheet, some with grids then some with just lengths.
A colleague of mine @DrPMaths made this impressive collection of triangles with 3 integer side lengths and an integer height. Again, they are a great way to check that students are identifying the perpendicular height and multiplying that by the base rather than just multiplying the numbers they are presented with. There are literally hundreds of them, this is a snapshot from somewhere near the beginning!