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