X+y=525 3x+7y=2775
a.340
b.280
c.225
d.300

C.225

Step-by-step explanation: for this case we need to calculate the value of x, to complete this we have 2 equations,

you can stat with simple equation X+y=525, if you clear x we get the following equation.

x = 525 - y

after that we are going to replace x in the major equation.

3x + 7y = 2775

After replace x we get the following equation

3 * (525 - y)  + 7y = 2775

after that, the 3 is going to multiply each value into the parenthesis

3 * 525 - 3 * + 7y = 2775

after resolve the product we get the following equation

1575 - 3y + 7y = 2775

you need resolve the equation with values which has the y

getting the following result

1575 + 4y = 2775

after that you pass the 1575 to the other side with the sign of subtraction

4y =  2775 - 1575

4y = 1200

after that, the 4 which is multiplying pass to the other side dividing

then

y = 1200/4

y = 300

finally, you will replace the value of y in the equation where we clear x, this equation.

x = 525 - y

if you replace y

x = 525 - 300

x = 225

then value of the x is 225

the median here is 25. your lowest value is 14 and highest value is 48. to find the third quartile, find the medium number in between 25 and 48 which would be 42 i believe.

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step-by-step explanation: