hey its very simple.........>
Tr+1 = 7Cr (x^7-r) (2^r) (1/x^2r)
Tr+1 = 7Cr (x^7-r-2r) (2^r)
Now,as we need coefficient of x^1..........so
x^7-3r = x^1
7-3r = 1
r=2............
now,putting value of r in general tern formula...........i-e,
Tr+1 = nCr (a^n-r) (b^r)
T2+1 = 7C2 (x^7-3(2)) (2^2)
T3 = (210 (x) (4)
so coefficient of x=21X4
x=84.............................answer
Hope u will get it