Gloves and heavy bag

suppose, the cost of a pair of MMA gloves is= $x$

so, the cost of one heavy bag will be = $2x+25$

now,

$x+2x+25=115$

or, $3x=115-25$

or, $x=\frac{90}{3}=30$

let $b$ and $g$ be the cost of one heavy bag and pair of gloves respectively, then

$b+g=115$ $\implies$ $b=115-g$ $\color{#D61F06}(1)$

and

$b=2g+25$ $\color{#D61F06}(2)$

Substitute $\color{#D61F06}(1)$ in $\color{#D61F06}(2)$ . we have

$115-g=2g+25$ $\implies$ $3g=90$ $\implies$ $\boxed{g=\$30}$