(1) This is a ternary linear equation system, and you can solve it by solving ternary linear equations (substitution and elimination). However, it is more common to calculate the same coefficients x and y directly from the equation. You directly add the equations 2x+4y = k, x-y = k+3 and x+y = 2 to get 4(x+y)=2k+5, that is, 8=2k+5 and k =1.5;

(2) Divide the number of big squares and small orthography each time, and add four squares each time (one big and three small, except the first one), so the nth figure has 4 (n-2)+7 = 4n-1;

Or count the number of large squares and small squares respectively, which are n and 2(n-2)+n- 1 (there are 2(n-2) non-overlapping squares and n- 1 overlapping squares), so there are 4n- 1 nth numbers;

Or do a few more data to find the rule directly, and the nth graph has 4n- 1.