Find parameter using independence

A question is this type if and only if it requires finding an unknown parameter (like x in a box of fruits) by setting up an equation using the independence condition or a given probability.

1 questions

CAIE S1 2019 June Q2
3 marks
2 Jameel has 5 plums and 3 apricots in a box. Rosa has \(x\) plums and 6 apricots in a box. One fruit is chosen at random from Jameel's box and one fruit is chosen at random from Rosa's box. The probability that both fruits chosen are plums is \(\frac { 1 } { 4 }\). Write down an equation in \(x\) and hence find \(x\). [3]