I can see no tile pattern.
x/7
g8
15-X
5+10 =15
n*5 - 6
Since there is no figure n, the number of triangles in it is described by the expression 0.
Let the number be x and so the expression is 4x -3
Let x be the unknown number. the expression is: x + 10.
It's a binomial algebraic expression that represents a number. The number that it represents completely depends on what number 'x' is.
An exponent.
x/7
An "expression" is anything that can be calculated to get a number, in other words, anything that represents a number, so that includes the numbers themselves.
g8
15-X
It can be: x-7
19x
9X + 7