The first equation is

The second equation is

If you sum the two equations you'll cancel y:

And since the sum must be 11, we have y=9.
B........................
we are given with 70 grams and is said that 48 grams is taken away. This is equal to 22 grams. To find the mass percentage, we divide the remaining mass and divide by the total mass. The remaining 22 grams is equal to 22/70 * 100 percent equal to 31.43 percent.
21000=a+b
ax.075xt=6xbx.04xt
t cancels out
a=3.2b
21000= 3.2b+b
21000=4.2b
b=5000
a=16000
account with 7.5% had 16000 invested in it.
account with 4% had 5000 invested in it
$90
50 for rent and equipment, 30 for wood and materials, 10 for delivery
50 + 30 + 10 = $90