Question

if a+x=15andx==5 then a=

Answer 1

Given - x = 5
a + x = 15
a = 15 - x
replacing value of x ,
a = 15 - 5 
a = 10

Answer 2

a+x=15 and x=5
now let us substitute the value of x in the equation,we get
a+5=15
=>a=15-5
a=10
Hope it helps...