Hi there,
The trapezoidal field's area is
(35+48) ÷ 2 × 26 = 1079 square yards
The triangular field's area is
39 × 26 ÷ 2 = 507 square yards
So totally, the area is
1079 + 507 = 1586 square yards
The farmer totally needs
1586÷150 ≈ 10.573
So he need at least 11 bags of fertilizer.
Hope this helped :P