Exponential functions are in the form

, where <em>a</em> is the initial value, <em>b</em> is the growth rate (percent increase) + 1, and <em>x</em> is the number of time periods. Our initial value is 100, and we're given the growth rate + 1 (tripling is the same as increasing by 200%; 200%=2.0; 2.0+1=3). Therefore our function is

.
You can say
x+y=5
x=5-y
You know the value of x, put it into the next equation.
3(5-y)-7y=19
15-3y-7y=19
15-19 = 10y
-4=10y
-4/10=y
-2/5=y
Put y value back into either equation to find value of x.
x+y=5
x-2/5=5
x=5+2/5
x=27/5
Therefore, x,y = (27/5, -2/5)
Hope I helped :)
Step 1. You must write down/ underline all the numbers given in the problem.
Step2. Identify all the unknown variable such as x, y, a, b [those are the most common ones].
Step 3 Identify what sign of operation your working with... It can be +,-,×,÷.
Step 3 write down all your terms on the LHS of the equation.
Step 4. Equate all the constant on the RHS of the equation. If the constant was negative It would be positive and vic versa
Step. Solve your problem