It is stipulated that x triangle y = 3x-2y, and known that x triangle (4 triangles 1) = 7

It is stipulated that x triangle y = 3x-2y, and known that x triangle (4 triangles 1) = 7

According to the meaning of the title
4 triangles 1
=3*4-2*1
=10
X triangle (4 triangles 1) = 7
X triangle 10 = 7
3x-2*10=7
3x=27
x=9