Respuesta :

What is the value of x in the proportion x + 1 / x+3 = 15/ 21
a.4
b.1/3
c.1/4
d.3
the answer is            
a.) 4
×+1/×+3=15/21
×+1=15(×+3)/21
×+1=15×+45/21
21(×+1)=15×+45
21×+21=15×+45
21×-15×=45-21
6×=24
×=4