Let 7x be the number of female visitors and 4y be the number of male visitors.


Then 3x is the number of girls and 4x is the number of adult females;

      y is the number of boys and 3y is the number of adult males.


Equations:

    7x + 4y = 1081,    (1)

     = 4x,     (2)

Equation (2) is the same as

    y = 4x.           (2')


Substitute (2') into (1)

    7x + 4*(4x) = 1081

    7x + 16x    = 1081

      23x       = 1081

        x       = 1081/23 = 47.


Hence,  y = 4*47 = 188.


ANSWER. The number of adult visitors was 4x + 3y = 4*47 + 3*188 = 752.

Hi
There were 1081 visitors at a museum. 3/7 of the female visitors and 1/4 of the male visitors were children. If the number of female adults was 1/3 of the number of male adults, how many adult visitors were at the museum. 

Let number of males and females, be M, and F, respectively
Since  of females were children, then  of females were adults
Since  of M (males), or  were children, then  of males were adults
Since number of female adults () was  the number of male adults (), we
get: 
   4(4F) = 7M ----- Cross-multiplying
     16F = 7M ----- eq (i)

There were 1,081 vistors, so we get:
   M + F = 1,081
       F = 1,081 - M ---- eq (ii)

        16(1,081 - M) = 7M --- Substituting 1,081 - M for F in eq (i)
      16(1,081) - 16M = 7M
            16(1,081) = 7M + 16M
            16(1,081) = 23M
Number of males, or 

As seen above, number of female adults = 
Also, number of male aduls = 
So, number of adults = female adults + male adults =