We don't know the exact number of squares and the number of triangle but only their total number, 10.

4 toothpicks to form one square and 3 toothpicks to form 1 triangle.

Guess any 2 numbers that add up to 10. Use these numbers of squares and triangles to find their number of toothpicks used.

Then add the number of toothpicks used to check against 36. If correct, the number of squares and number of triangles is guessed correctly.