Answer:
11
Explanation:
x = 11
10 10+ x
-------- = ------------
12 21
using cross products
12*21 = 12 *(10+x)
252 = 120 + 12x
subtract 120 from each side
252-120 = 120-120 + 12x
132 = 12x
divide by 12
132/12 =12x/12
11 = x
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