Answer:
[tex] 400009 \times {10}^{8} [/tex]
Step-by-step explanation:
[tex](4 \times {10}^{13} ) + (9 \times {10}^{8} ) \\ \\ = (400000 \times {10}^{8} ) + (9 \times {10}^{8} ) \\ \\ = (400000 + 9) \times {10}^{8} \\ \\ = 400009 \times {10}^{8} [/tex]
