let

x = the first number

y = the second number

THREE TIMES A FIRST NUMBER DECREASED BY A SECOND NUMBER IS 25:

3x - y = 25

THE FIRST NUMBER INCREASED BY THREE TIMES THE SECOND NUMBER IS -5:

x + 3y = -5

by solving the system of equations:

3x - y = 25

x + 3y = -5

we find:

x = 7

y = -4

click here to see the step by step solution of the system of equations:

the first number is 7 and the second number is -4.