solving equation variation, they are of tow types.
we have direct and inverse variation.
this question is a direct variation
the formula for direct variation is
y = kx
where the value of k is a nonzero constant greater than zero
so given,
y = 15
x = 3
recall,
y = kx
imputing values given
15 = 3k
dividing both side by 3
k = 15/3
k = 5
so finding y when k = 15
y = kx
so,
y = 5(15)
y = 75