Step 1: Multiply the first two binomials
(5x + 6y) (7a - 9d) = 35ax - 45dx + 42ay -54dy
Step 2: Multiply the result the result by the third binomial:
(3f-8g) (35ax - 45dx + 42ay -54dy)
= 105afx - 135dfx + 126afy - 162dfy - 280agx + 360dgx - 336agy + 432dgy
