Answer:
x=15
Step-by-step explanation:
21:2x=7:10 can be rewritten as 21/2x=7/10
21/2x=7/10, cross multiply
= 14x=210
This can be expanded to x⁴ - 6x²
13²+4−1
<em><u>hope it helps</u></em>
Is that the full question, because it doesn't make sense to me :/