John has four more nickels than dimes in his pocket, for a total of $1.25. which equation could be used to determine the numbet of dimes, x, in his pocket?

So, you have to have your equation in terms of dimes. What you said about what he has: four more nickels than dimes in his pocket. Will help with our equation.
We know what a nickel and dime is worth. A nickel is .05 and a dime is .1
We don't know how many dimes are in his pocket, since we're trying to solve it.
.1x+(4+x).05=1.25; 
In the parenthesis, it shows how there are four more nickels. Let's solve it now.
.1x + (4+x).05=1.25
.1x + .2+ .05x = 1.25; Let's add like terms.
.15x + .2 = 1.25; Subtract .2 from both sides.
.15x= 1.05
1.05÷.15= 7 =x
There are 7 dimes in his pocket, let's check our answer.
We now know there are 11 nickels, since there are four more nickels than dimes.
11(.05) +.1(7) = 1.25
.55+ .7 = 1.25
Now that we've tried it, we know there are 7 dimes in his pocket.
Tell me if this helps!