Question 4291
First: Assign the variables.

Let x = the amount invested in the savings account @ 3%
Let y = the amount invested in the mutual fund @ 25%

Second: Write the sytem of equations.  Change the percents to their decimal equivalents.  3% = 0.03   25% = 0.25

0.03x + 0.25y = $5,150.00  Total interest earned.
x + y = $25,000.00         Total amount invested.  Rewite as x = $25,000.00 - y and substitute for x in the first equation.

0.03($25,000.00 - y) + 0.25y = $5.150.00     Solve for y.
$750.00 - 0.03y + 0.25y = $5,150.00   Simplify.
$750.00 + 0.22y = $5,150.00     Subtract $750.00 from both sides.
0.22y = $4,400.00   Divide both sides by 0.22
 y = $20,000.00   Now find x.
x = $25,000 - y
x = $25,000.00 - $20,000.00
x = $5,000.00

Juan invested $5,000.00 in the savings account @ 3% interest, and $20,000.00 in the mutual fund @ 25% interest.

Check:  0.03($5,000.00) + 0.25($20,000.00) = $150.00 + $5,000.00 = $5,150.00