Answer:
243
Step-by-step explanation:
[tex]5( \sqrt{ {x}^{2} + 2x - 14} + x) = 20 \\ \\ \sqrt{ {x}^{2} + 2x - 14} + x= \frac{20}{5} \\ \\ \sqrt{ {x}^{2} + 2x - 14} + x= 4 \\ \\ \sqrt{ {x}^{2} + 2x - 14} = 4 - x\\ \\ {(\sqrt{ {x}^{2} + 2x - 14} )}^{2} = {(4 - x)}^{2} \\ \\ \cancel{ {x}^{2}} + 2x - 14 = 16 - 8x + \cancel{ {x}^{2} } \\ \\ 2x - 14 = 16 - 8x \\ \\ 2x + 8x = 16 + 14 \\ \\ 10x = 30 \\ \\ x = \frac{30}{10} \\ \\ x = 3 \\ \\ 3 {x}^{4} = 3 {(3)}^{4} = 3 \times 81 \\ \\ \huge \red {3 {x}^{4}= 243}[/tex]
