Devi has a grid in the shape of a parallelogram. she has equilateral triangles. each equilateral triangle has an area of 40 square millimeters and each equilateral triangle fits on the grid.

if the base of the grid is 26 centimeters and the height is 10 centimeters, how many triangles can devi fit on the grid?

The answer is 65
there are 10 millimeters in every centimeter...so to get the size of the grid, you multiply 260 x 10 to get 260 centimeters and then to see how many millimeters are in the 260 centimeter grid you multiply it by 260 by 10, which gives you 2,600 millimeters, so then all that is left to do is divide 2,600 millimeters by 40 millimeters for each of her 40 millimeter equilateral triangles to see how many will fit...the answer is 65  

The third and fourth box.