1. Last year, Andy invested $5000 in company X, $4000 in company Y and $3000 in company Z. He made a profit of $850 for the year.
During the same time period, Bryan invested $4500 in company X, $900 in company Y and $3600 in company Z. He made a profit of $657 for the year.
Similarly, Charles invested $4000 in company X, $2400 in company Y and $1600 in company Z. He made a profit of $552 for the year.
If Mary invested $2800 in company X, how much profit will she make for the year?
I divide the first one by 1000 and the second by 300 and the third by 400
now it is easy to solve multiply the first by -3 and add it to the second
you have an equation with two variable then multiply the first one with -2 and add it yo the third you will get two equation just with y,z solve them .
best wishes