Answer:
let x be no. of 4-wheel and y be no. of 3-wheel ATVs
so
x+y=17 (each has one set of handlebars)
4*x + 3*y = 61
4*(x)+3*(17-x)=61
x=61-51=10
y=17-10=7
thus x=10 and y=7 and that's your answer