Chapter 22 - Gauss's Law - Problems - Exercises - Page 745: 22.2

$ \Phi_{E} = 7.40 \mathrm{N} \cdot \mathrm{m}^{2} / \mathrm{C}$

The electric flux, in this case, will be \begin{aligned} \Phi_{E} &=E A \cos \phi \\ &=(90 \mathrm{N} / \mathrm{C})(0.4 \mathrm{m} \times 0.6 \mathrm{m})\cos \left(90^{\circ} - 20^{\circ} \right)\\ & =\boxed{7.40 \mathrm{N} \cdot \mathrm{m}^{2} / \mathrm{C}} \end{aligned}