If $f(x)=sqrtx$ , $g(x)=7x+b$ and $f(g(x))$ passes through $(4,6)$ , what is $b$ ?

Question

A $8$
B $26$
C $6$
D $4$

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Answer 1 · 2017-03-17T06:22:36

Answer is A.

As $f(x)=sqrtx$ and $g(x)=7x+b$ .

$y=f{g(x)}=sqrt(7x+b)$

As it passes through $(4, 6)$

$6=sqrt(7xx4+b)$ and squaring both sides, we get

$36=28+b$

or $b=36-28=8$

Hence, answer is A.