a) 15
b) 100
~HT~
k cho mik nha
\(a,49:x+56:x=7\)
\(\Rightarrow\left(49+56\right):x=7\)
\(\Rightarrow105:x=7\)
\(\Rightarrow x=15\)
Vậy: \(x=15\)
\(b,390:x-90:x=3\)
\(\Rightarrow\left(390-90\right):x=3\)
\(\Rightarrow300:x=3\)
\(\Rightarrow x=100\)
Vậy: \(x=100\)