in a rhombus, the diagonals bisect each other, namely they cut each other in halves, and also they cut their vertices in half too.
what does that mean? well, it means that the two angles at the vertex F are twins, thus 8x - 49 = 5x - 7.

now, the diagonals in a rhombus also meet each other at a right angle, therefore, on the triangle FIG, ∡F is 63°, ∡I is 90° and ∡G is 180 - ∡F - ∡I.